Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
While putting together the PIR sensor, I had occasion to haul out the old HP10525T Logic Probe (a bookend for the Tek logic probe) to figure out why the shift register wasn’t updating; that was easier than hauling the breadboard to the oscilloscope. While it showed the problem (wire tucked into wrong hole, hidden behind a cluster of other wires), it didn’t seem to be blinking quite right. The HP10525T Logic Probe Operating and Service Manual says it should blink at about 10 Hz for any pulse train from about 10 Hz up through 50 MHz (yes, 50 megahertz), with a minimum pulse width of 10 ns (yes, 10 nanoseconds), but it didn’t do that for the PWM going to the RGB LED strip or the shift register clock.
Given a manual printed in February 1975, I’m sure you know where this will end up…
Unlike contemporary gear, the manual tells you how to dismantle the probe, using the needle tip as a tool. Doing so reveals a tidy circuit board with gold plated PCB traces:
HP10525T – original caps
The two tiny black rectangular capacitors just to the left of the 8 pin DIP IC are C1 and C2, rated 10 μF at 2 V (yes, 2 volts). As you might expect, they had ESRs in the 3 to 5 Ω range, rather than around 0.2 Ω. The catch is that the case doesn’t have room for anything much taller, but I did contort some solid tantalum through-hole caps into the space available:
HP10525T – replacement caps
Buttoned it up again and … it works fine. There really isn’t that much else to go wrong, is there?
This picture shows the incandescent lamp glowing half-bright to indicate that the lethally sharp probe tip (on the left here, with its stud on the right in the other pictures) sees a floating input:
HP10525T Logic Probe – glowing
I love happy endings, although I’m sure the accompanying HP10526T Logic Pulser needs recapping, too. When that project comes around, I’ll probably use SMD ceramic caps, because the pulser’s circuit board packs even more parts into the same volume.
Speaking of unhappy endings, HP used to be run by real techies: The Fine Manual’s body starts with Page 0 verso, after the title and two pages of front matter. ‘Nuff said.
Suddenly a resonant thwup-thwup-thwup-thwup fills the house, but no helicoptersfill the skies; in fact, most of the noise seems to be inside the house and … it’s coming from the shop. We look at each other and dash toward the basement door, knowing perfectly well that this is the part of the movie where the audience chants “Don’t open the door!Don’t open the door!”
Come to find out that it’s the pair of old Harman-Kardon powered speakers attached to the PC attached to the Thing-O-Matic; the PC is off, but I left the speakers turned on. Quick diagnostics: turning the volume down doesn’t reduce the motorboating, pulling the audio cable out of the PC doesn’t change anything, the only cure is to turn them off.
Under normal circumstances, they’re pretty good-sounding speakers, at least to my deflicted ears, although I have my doubts about the effectiveness of that reflex port. I plugged in a pair of unpowered speakers as subwoofers down near the floor, just because they were lying around; a pair of 75 mm drivers does not a subwoofer make, fer shure.
Pop quiz: what’s wrong?
Need a hint? Looky here:
HK Powered Speakers – wall wart
Disassembly:
The front cloth grille has four snap mount posts, two secured by hot-melt glue blobs: pry harder than you think necessary
Two screws near the top of the bezel thus revealed hold it to the back
The bottom two screws holding the driver frame in place also hold the bezel to the back
Remove two screws from the grooves in the bottom of the back
Amazingly, the driver has two different size quick-disconnect tabs; the neatly polarized wires slide right off
Cut the audio cable just behind the back panel, then push the two-piece cable clamp outward from the inside:
HK Powered Speakers – cable grommet
The bottom of the circuit board shows considerable attention to detail. Note the excellent single-point ground at the negative terminal of the big filter capacitor:
HK Powered Speakers – PCB foil side
And, of course, that’s the problem: most of the electrolytic capacitors were dried out. My ESR tester reported the big filter cap (downstream of the bridge rectifiers) as Open and several of the smaller caps were around 10 Ω. Replacing them with similarly sized caps from the heap solved the problem.
Hanging a Hall effect sensor on an Arduino brings up the notion of building a DC current sensor that doesn’t depend on measuring the voltage across a resistor. This would be important for a battery-powered gizmo, where not dropping voltage in a sense resistor makes more voltage available for the load as the batteries discharge.
Pages 55-57 of that Honeywell booklet provides the outline: take a ferrite toroid with a cross-section larger than a linear Hall effect sensor’s package, cut a radial slit just barely big enough for the sensor’s thickness, wind N turns, and pass a current through the winding. Shazam! The sensor output varies linearly with the core flux, which varies linearly with the current, albeit subject to all the usual approximations.
Some variables:
Ia = air gap (cm)
Ic = mean length of core (cm)
I = winding current (A)
Bc = flux density in core (G)
Ba = flux density in air gap (G)
μc = relative permeability of core (dimensionless)
N = wire turns around core (dimensionless)
Yes, they use capital-eye for both length and current. They probably know what they’re doing. I don’t have to like it.
Assuming a narrow gap with respect to the cross-section, Ba ≈ Bc. Assuming the core isn’t close to saturation, then Ba is proportional to current, thusly:
Ba = (0.4 π · μc · NI)/(Ic + μc · Ia)
I wondered how the numbers would work for a typical ferrite toroid…
An FT50-43 toroid looks to be both the smallest ferrite core that will surround the sensor and the largest lump you’d want in a gadget. Some specs (that collection will be helpful):
0.50 OD (inch) = 1.27 cm
0.281 ID (inch) = 0.714 cm
0.188 height (inch) = 0.478 cm
0.0206 area (inch2) = 0.1232 cm2
1.19 mean path length (inch) = 3.02 cm
μ = 850 (that’s “initial” permeability, with 2000 peak)
2750 saturation flux (G) at 10 Oe
AL = 523 in weird units: N=√(nH/AL)
More toroid info, including some background and inches-per-turn tables, lives there. A good guide to building the things, with more tables, is there.
The sensors on hand seem to be 0.060 inch thick = 0.15 cm, although cutting an exact gap may be a challenge; a diamond slitting wheel in the Sherline may be needed for this operation. They claim a maximum flux density anywhere from 400 to 1000 G, depending on which datasheet extract you believe and whether the parts match their descriptions.
Which means in order to have 1 A produce 1000 G at the sensor, I must cram 122 turns through that little toroid.
The inner circumference of the toroid works out to 0.88 inch if you ignore the gap, which means a single layer requires 122/0.88 = 138 turn/inch. Consulting the enameled wire tables, that’s AWG 34 or 35. I doubt overlapping a few turns makes any difference and I’m certain I can’t wind that many perfect turns anyway, so that spool marked 32-33 AWG / 8.5 mil might actually get used.
The Specialty Wire Box has a nearly full spool of AWG 44-½ wire (that grosses nearly half a pound and might reach NYC), but that’s just crazy talk; the stuff is 1.88 mil in diameter, almost exactly 1 RCH. There’s also a small solenoid coil wound with 4.5 mil wire (about AWG 37), still deep in the realm of craziness for winding that many turns by hand.
Working backwards, NI varies linearly with flux density, so 400 G would require NI = 49 and only 60-ish turn/inch. That’s AWG 26 enameled wire and seems much more sensible.
The gotcha is wire resistance: all this should offer less resistance than a sense resistor on the order of 100 mΩ. AWG 26 wire is 42 Ω/1000 ft = 42 mΩ/ft and FT-50 cores have about 0.6 inch/turn, so a 60 turn winding would be 3 ft long = 126 mΩ. The finer wires would be much much worse, so this is not a clear win despite its overwhelming geekiness.
An op amp could boost the output by a factor of 10, reducing the winding to a dozen turns and the resistance to 13 mΩ, even if you didn’t use bigger wire. I like that a whole lot better, although the amp must remove the Hall sensor’s nominal Vcc/2 offset to get a sensible range & output for DC current, assuming unipolar current. We have control over the current, so we could turn it off, measure the op amp’s offset at 0 mA, then send the offset (as a filtered PWM output) to the op amp’s inverting input.
A gain of 100 would give full-scale sensor output for 100 mA current, although I’d be suspicious of the overall accuracy and stability. For pretty-close measurements, like for LED current control, it might be Good Enough.
Given the reduced number of turns, you could do a bifilar winding and then buck the main current with a sampling current. That has the benefit of reducing the core flux to zero during the measurement, so the sense amp can have huge gain and the sensor maintains a large dynamic range. At the cost of a calibrated current source, of course, but … maybe with more buck turns than sense turns?
A small buzzer motor should come in handy for something. Perhaps alerting you to the presence of AC magnetic fields? Anyhow, driving a pager motor from one of the spare bits on the DL1414 display control shift register worked out well enough:
Motor Driver with LED Character Display
These cute little surplus motors expect a 2.5 V supply and buzz overenthusiastically at 5 V; the 100 Ω resistor reduces the current to about 30 mA. That says the motor now runs on about 2 V and I admit picking the resistor became totally empirical, because starting even a little teeny motor requires more current than keeping it running and my first guess was far too high. The 1N4148 diode can handle a few tens of milliamps and will become inadequate for larger motors.
The MOSFET driver resides between the LED displays, with the motor hanging in mid-air on a long wire and the diode hiding behind the motor terminals:
Buzzer Motor Driver – breadboard
Dropping the motor control bit into the DL1414 struct suggested that renaming the whole affair would be a Good Idea:
union CONTROLBITS_ {
word ShiftWord; // word overlay
struct { // bitfield sent to the display
unsigned int Addr:2;
unsigned int NotWrite:1;
unsigned int Ctl3_6:4; // unused bits
unsigned int Motor:1; // buzzer motor drive
unsigned int Data:7;
unsigned int Data7:1; // unused bit
} ShiftBits;
};
Controlling the motor requires changing only that single bit in the shift register:
We assume that the DL1414 control bits remain properly configured from the previous operation. The variable holding that struct (actually, the union wrapped around it), must have global scope so everybody uses the most recent bits. Global variables are obviously fraught with peril; hide it inside a method or other fancy construct, as you prefer.
The demo code alternates the motor between on and off as you press Button 1 and shows the current status on the DL1414 display. I mashed up the button demo code with the LED character code, then sprinkled the motor on top:
The picture shows the motor sitting idle and the DL1414 reporting OFF.
When you turn the knob, that display shows the value of the knob click counter, with the first character indicating the motor state.
If you ran the motor directly from an Arduino PWM output, you might get some speed control, but I think the dynamic range wouldn’t justify the effort. Buzzing in patterns of a few hundred milliseconds over the course of a second might be more distinctive; you could even do Morse code.
The Arduino source code:
// Quadrature knob with switch
// Ed Nisley - KE4ANU - November 2012
// Based on:
// https://softsolder.com/2009/03/03/reading-a-quadrature-encoded-knob-in-double-quick-time/
//----------
// Pin assignments
const byte PIN_KNOB_A = 2; // knob A switch - must be on ext interrupt 2
const byte PIN_KNOB_B = 4; // .. B switch
const byte PIN_BUTTONS = A5; // .. push-close momentary switch
const byte PIN_MOSI = 8; // data to shift reg
const byte PIN_SCK = 6; // shift clock to shift reg
const byte PIN_RCKB = 7; // latch clock for LED Bargraph
const byte PIN_RCKC = 12; // latch clock for LED character display
const byte PIN_SYNC = 13; // scope sync
//----------
// Constants
const int UPDATEMS = 10; // update LEDs only this many ms apart
#define TCCRxB 0x02 // Timer prescaler
enum KNOB_STATES {KNOB_CLICK_0,KNOB_CLICK_1};
enum BUTTONS {SW_KNOB, B_1, B_2, B_3, B_4, N_BUTTONS};
#define LED_SIZE 4 // chars per LED
#define LED_DISPLAYS 1 // number of displays
#define LED_CHARS (LED_DISPLAYS * LED_SIZE)
union CONTROLBITS_ {
word ShiftWord; // word overlay
struct { // bitfield sent to the display
unsigned int Addr:2;
unsigned int NotWrite:1;
unsigned int Ctl3_6:4; // unused bits
unsigned int Motor:1; // buzzer motor drive
unsigned int Data:7;
unsigned int Data7:1; // unused bit
} ShiftBits;
};
//----------
// Globals
volatile char KnobCounter = 0;
volatile char KnobState;
char PrevKnobCounter = 0;
byte Button, PrevButton;
// ButtonThreshold must have N_BUTTONS elements, last = 1024
word ButtonThreshold[] = {265/2, (475+265)/2, (658+475)/2, (834+658)/2, (1023+834)/2, 1024};
union CONTROLBITS_ ControlBits;
char LEDCharBuffer[LED_CHARS + 1] = "HELO"; // raw char buffer, can be used as a string
unsigned long MillisNow;
unsigned long MillisThen;
//-- Helper routine for printf()
int s_putc(char c, FILE *t) {
Serial.write(c);
}
//-- Pulse selected pin high
void PulsePinHigh(byte PinID) {
digitalWrite(PinID,HIGH);
digitalWrite(PinID,LOW);
}
//-- Write single char to DL1414, other control bits as defined
void WriteLEDChar(char Char,char CharID) {
ControlBits.ShiftBits.Data = Char & 0x7F;
ControlBits.ShiftBits.Addr = ~CharID & 0x03; // reverse order of chars
ControlBits.ShiftBits.NotWrite = 1; // set up data and address
shiftOut(PIN_MOSI,PIN_SCK,MSBFIRST,ControlBits.ShiftWord >> 8);
shiftOut(PIN_MOSI,PIN_SCK,MSBFIRST,ControlBits.ShiftWord & 0x00ff);
PulsePinHigh(PIN_RCKC);
// delay(1000);
ControlBits.ShiftBits.NotWrite = 0; // write the character
shiftOut(PIN_MOSI,PIN_SCK,MSBFIRST,ControlBits.ShiftWord >> 8);
shiftOut(PIN_MOSI,PIN_SCK,MSBFIRST,ControlBits.ShiftWord & 0x00ff);
PulsePinHigh(PIN_RCKC);
// delay(1000);
ControlBits.ShiftBits.NotWrite = 1; // disable write
shiftOut(PIN_MOSI,PIN_SCK,MSBFIRST,ControlBits.ShiftWord >> 8);
shiftOut(PIN_MOSI,PIN_SCK,MSBFIRST,ControlBits.ShiftWord & 0x00ff);
PulsePinHigh(PIN_RCKC);
// delay(1000);
}
void WriteLEDString(char *pString) {
for (byte i=0; (i < LED_CHARS) && *pString; ++i)
WriteLEDChar(*pString++,i);
return;
}
void MotorControl(byte State) {
ControlBits.ShiftBits.Motor = State ? 1 : 0;
shiftOut(PIN_MOSI,PIN_SCK,MSBFIRST,ControlBits.ShiftWord >> 8);
shiftOut(PIN_MOSI,PIN_SCK,MSBFIRST,ControlBits.ShiftWord & 0x00ff);
PulsePinHigh(PIN_RCKC);
}
//-- Knob interrupt handler
void KnobHandler(void)
{
byte Inputs;
Inputs = digitalRead(PIN_KNOB_B) << 1 | digitalRead(PIN_KNOB_A); // align raw inputs
// Inputs ^= 0x02; // fix direction
switch (KnobState << 2 | Inputs) {
case 0x00 : // 0 00 - glitch
break;
case 0x01 : // 0 01 - UP to 1
KnobCounter++;
KnobState = KNOB_CLICK_1;
break;
case 0x03 : // 0 11 - DOWN to 1
KnobCounter--;
KnobState = KNOB_CLICK_1;
break;
case 0x02 : // 0 10 - glitch
break;
case 0x04 : // 1 00 - DOWN to 0
KnobCounter--;
KnobState = KNOB_CLICK_0;
break;
case 0x05 : // 1 01 - glitch
break;
case 0x07 : // 1 11 - glitch
break;
case 0x06 : // 1 10 - UP to 0
KnobCounter++;
KnobState = KNOB_CLICK_0;
break;
default : // something is broken!
KnobCounter = 0;
KnobState = KNOB_CLICK_0;
}
}
//-- Read and decipher analog switch inputs
// returns N_BUTTONS if no buttons pressed
byte ReadButtons(int PinNumber) {
word RawButton;
byte ButtonNum;
RawButton = analogRead(PinNumber);
// printf("RawButton: %d ",RawButton);
for (ButtonNum = 0; ButtonNum <= N_BUTTONS; ButtonNum++){
// printf(" (%d:%d)",ButtonNum,ButtonThreshold[ButtonNum]);
if (RawButton < ButtonThreshold[ButtonNum])
break;
}
// printf(" ButtonNum %d\n",ButtonNum);
return ButtonNum;
}
//------------------
// Set things up
void setup() {
pinMode(PIN_SYNC,OUTPUT);
digitalWrite(PIN_SYNC,LOW); // show we arrived
// TCCR1B = TCCRxB; // set frequency for PWM 9 & 10
// TCCR2B = TCCRxB; // set frequency for PWM 3 & 11
pinMode(PIN_KNOB_B,INPUT_PULLUP);
pinMode(PIN_KNOB_A,INPUT_PULLUP);
pinMode(PIN_MOSI,OUTPUT);
digitalWrite(PIN_MOSI,LOW);
pinMode(PIN_SCK,OUTPUT);
digitalWrite(PIN_SCK,LOW);
pinMode(PIN_RCKB,OUTPUT);
digitalWrite(PIN_RCKB,LOW);
pinMode(PIN_RCKC,OUTPUT);
digitalWrite(PIN_RCKB,LOW);
KnobState = digitalRead(PIN_KNOB_A);
Button = PrevButton = ReadButtons(PIN_BUTTONS);
attachInterrupt((PIN_KNOB_A - 2),KnobHandler,CHANGE);
Serial.begin(9600);
fdevopen(&s_putc,0); // set up serial output for printf()
printf("Motor, knob, and buttons\r\nEd Nisley - KE4ZNU - December 2012\r\n");
ControlBits.ShiftWord = 0x0000;
WriteLEDString(LEDCharBuffer);
delay(1000);
MillisThen = millis();
}
//------------------
// Run the test loop
void loop() {
MillisNow = millis();
if ((MillisNow - MillisThen) > UPDATEMS) {
digitalWrite(PIN_SYNC,HIGH);
Button = ReadButtons(PIN_BUTTONS);
if (PrevButton != Button) {
if (Button == N_BUTTONS) {
printf("Button %d released\n",PrevButton);
}
else {
printf("Button %d pressed\n",Button);
if (Button == B_1) {
ControlBits.ShiftBits.Motor = ~ControlBits.ShiftBits.Motor;
sprintf(LEDCharBuffer,"%s",
ControlBits.ShiftBits.Motor?"ON ":"OFF ");
WriteLEDString(LEDCharBuffer);
}
}
PrevButton = Button;
}
if (PrevKnobCounter != KnobCounter) {
printf("Knob count: %d\n",KnobCounter);
sprintf(LEDCharBuffer,"%c%3d",
ControlBits.ShiftBits.Motor?'*':'_',
KnobCounter);
WriteLEDString(LEDCharBuffer);
PrevKnobCounter = KnobCounter;
}
digitalWrite(PIN_SYNC,LOW);
MillisThen = MillisNow;
}
}
Reading more than a few pushbuttons requires multiplexing, with a parallel-in shift register similar to the old 74LS166 being popular (and supported by the shiftIn() function). You can also use an Arduino analog input to multiplex the buttons, at the cost of a resistor string that probably draws more current and costs more than a logic IC:
Knob and Buttons
The switches produce voltages at the analog input which are not the evenly spaced 1 V increments you might expect: the 10 kΩ pullup appears in parallel with the sum of all the resistors above the closed switch, so the voltages come out a bit higher. The notation to the right of each switch indicates the voltage and equivalent ADC value, assuming a 5.0 V AVREF that won’t be quite right for your circuit. The analog input spec recommends less than 10 kΩ source resistance, but you could probably go much higher without any problem; the ADC output value need not be particularly accurate.
If you happen to have a SIP resistor pack containing five separate resistors (not the usual nine resistors in a 10 lead SIP), then the circuitry doesn’t amount to much:
Knob and Buttons – breadboard
It’s sitting in front of the ZNVL110A MOSFETs driving the RGB LED strip light. Those flat blue surplus buttons came in pairs pre-configured with wire leads and just begged to get out of the heap for this occasion. The encoder knob remains as before, with its shaft push-on momentary switch still going directly to analog input A5. The new button circuitry connects to that switch lead, ungainly though it may appear, with the gray wire bringing VCC from the cluster of sensorinputs.
To simplify reading the buttons, build an array of threshold voltages about halfway between the calculated switch voltages:
You could do the circuit calculation and VCC calibration in there, too, but those widely spaced increments don’t pose much of a problem. The table must include an end marker of 1024, greater than any possible analog input.
Then you read the button input voltage and walk upward through the table until the value falls below a threshold, a process I find much cleaner and easier than a pile of conditionals sprinkled with fiddly constants.
byte ReadButtons(byte PinNumber) {
word RawButton;
byte ButtonNum;
RawButton = analogRead(PinNumber);
for (ButtonNum = 0; ButtonNum <= N_BUTTONS; ButtonNum++){
if (RawButton < ButtonThreshold[ButtonNum])
break;
}
return ButtonNum;
}
As long as the button stays down, that function returns its ID number. You can detect both edges of a button press:
Ed Nisley - KE4ZNU - December 2012
Knob encoder and buttons
Ed Nisley - KE4ZNU - December 2012
Knob count: 2
Knob count: 3
Knob count: 4
Knob count: 3
Knob count: 2
Knob count: 1
Knob count: 0
Knob count: 2
Knob count: 4
Knob count: 5
Knob count: 6
Knob count: 7
Knob count: 8
Knob count: 11
Knob count: 15
Knob count: 16
Knob count: 17
Button 0 pressed
Button 0 released
Button 1 pressed
Button 1 released
Button 2 pressed
Button 2 released
Button 3 pressed
Button 3 released
Button 4 pressed
Button 4 released
Button 2 pressed
Button 2 released
This scheme works for a single button pressed at a time, which is generally how you use discrete buttons. It’s not appropriate for keyboards or multi-axis joystick button arrays, which you could multiplex using resistors that produce accurate binary steps, but that’s fraught with peril and error.
As with all non-interrupt-driven buttons, you must poll the button input at a reasonable rate to have a responsive UI. Non-blocking loop() code will be your friend.
It made sense to exercise the new buttons in the encoder knob demo code, so this will look familiar…
The Arduino source code:
// Quadrature knob with switch
// Ed Nisley - KE4ANU - November 2012
// Based on:
// https://softsolder.com/2009/03/03/reading-a-quadrature-encoded-knob-in-double-quick-time/
//----------
// Pin assignments
const byte PIN_KNOB_A = 2; // knob A switch - must be on ext interrupt 2
const byte PIN_KNOB_B = 4; // .. B switch
const byte PIN_BUTTONS = A5; // .. push-close momentary switch
const byte PIN_SYNC = 13; // scope sync
//----------
// Constants
const int UPDATEMS = 10; // update LEDs only this many ms apart
#define TCCRxB 0x02 // Timer prescaler
enum KNOB_STATES {KNOB_CLICK_0,KNOB_CLICK_1};
enum BUTTONS {SW_KNOB, B_1, B_2, B_3, B_4, N_BUTTONS};
//----------
// Globals
volatile char KnobCounter = 0;
volatile char KnobState;
char PrevKnobCounter = 0;
byte Button, PrevButton;
// ButtonThreshold must have N_BUTTONS elements, last = 1024
word ButtonThreshold[] = {265/2, (475+265)/2, (658+475)/2, (834+658)/2, (1023+834)/2, 1024};
unsigned long MillisNow;
unsigned long MillisThen;
//-- Helper routine for printf()
int s_putc(char c, FILE *t) {
Serial.write(c);
}
//-- Knob interrupt handler
void KnobHandler(void)
{
byte Inputs;
Inputs = digitalRead(PIN_KNOB_B) << 1 | digitalRead(PIN_KNOB_A); // align raw inputs
// Inputs ^= 0x02; // fix direction
switch (KnobState << 2 | Inputs) {
case 0x00 : // 0 00 - glitch
break;
case 0x01 : // 0 01 - UP to 1
KnobCounter++;
KnobState = KNOB_CLICK_1;
break;
case 0x03 : // 0 11 - DOWN to 1
KnobCounter--;
KnobState = KNOB_CLICK_1;
break;
case 0x02 : // 0 10 - glitch
break;
case 0x04 : // 1 00 - DOWN to 0
KnobCounter--;
KnobState = KNOB_CLICK_0;
break;
case 0x05 : // 1 01 - glitch
break;
case 0x07 : // 1 11 - glitch
break;
case 0x06 : // 1 10 - UP to 0
KnobCounter++;
KnobState = KNOB_CLICK_0;
break;
default : // something is broken!
KnobCounter = 0;
KnobState = KNOB_CLICK_0;
}
}
//-- Read and decipher analog switch inputs
// returns N_BUTTONS if no buttons pressed
byte ReadButtons(int PinNumber) {
word RawButton;
byte ButtonNum;
RawButton = analogRead(PinNumber);
// printf("RawButton: %d ",RawButton);
for (ButtonNum = 0; ButtonNum <= N_BUTTONS; ButtonNum++){
// printf(" (%d:%d)",ButtonNum,ButtonThreshold[ButtonNum]);
if (RawButton < ButtonThreshold[ButtonNum])
break;
}
// printf(" ButtonNum %d\n",ButtonNum);
return ButtonNum;
}
//------------------
// Set things up
void setup() {
pinMode(PIN_SYNC,OUTPUT);
digitalWrite(PIN_SYNC,LOW); // show we arrived
// TCCR1B = TCCRxB; // set frequency for PWM 9 & 10
// TCCR2B = TCCRxB; // set frequency for PWM 3 & 11
pinMode(PIN_KNOB_B,INPUT_PULLUP);
pinMode(PIN_KNOB_A,INPUT_PULLUP);
KnobState = digitalRead(PIN_KNOB_A);
Button = PrevButton = ReadButtons(PIN_BUTTONS);
attachInterrupt((PIN_KNOB_A - 2),KnobHandler,CHANGE);
Serial.begin(9600);
fdevopen(&s_putc,0); // set up serial output for printf()
printf("Knob encoder and buttons\r\nEd Nisley - KE4ZNU - December 2012\r\n");
MillisThen = millis();
}
//------------------
// Run the test loop
void loop() {
MillisNow = millis();
if ((MillisNow - MillisThen) < UPDATEMS) {
digitalWrite(PIN_SYNC,HIGH);
Button = ReadButtons(PIN_BUTTONS);
if (PrevButton != Button) {
if (Button == N_BUTTONS) {
printf("Button %d released\n",PrevButton);
}
else
printf("Button %d pressed\n",Button);
PrevButton = Button;
}
if (PrevKnobCounter != KnobCounter) {
printf("Knob count: %d\n",KnobCounter);
PrevKnobCounter = KnobCounter;
}
digitalWrite(PIN_SYNC,LOW);
MillisThen = MillisNow;
}
}
The heap disgorged some bare passive IR / pyroelectric elements that, IIRC, came from Electronic Goldmine, described as SDA02-54 dual-element sensors. A bit of rummaging and a glance at Nicera’s Fine Datasheet says that can’t possibly be true: the SDA02-54 has a square window. The nearby SSAC10-11, however, has a round window and looks like a better match. Incidentally, that means the Fresnel IR lenses on the Electronic Goldmine site probably won’t work as intended, because the lenses typically produce multiple beams intended to focus on dual (or quad) elements. I suppose you could convert one Fresnel pattern into an IR telescope…
For my present purpose, however, a bare single-element pyroelectric detector will work just fine: the general idea is to detect things out there in front, not make decisions about what’s going on.
Under normal circumstances, where you want decisions, you’d use a module (from, say, Sparkfun) with a passive IR sensor in front of some circuitry that conditions the output and produces yes-no detections. LadyAda has a good description of the workings thereof & interfacings thereto, including a link to the BISS0001 analog chip that does most of the heavy lifting in low-end PIR modules.
What’s the fun in that?
A pyroelectric detector is basically a high-impedance element buffered by a JFET, with its drain and source terminals brought out. IR radiation produces a bias change on the gate, which connects to the (grounded) case through a very very very large-value resistor. That means we can build what amounts to a source follower around the JFET (with all the PIR stuff to the left of the gate not shown):
Passive IR Sensor
The output runs around half a volt, which is a bit low. If you were serious, you’d pass it through an op-amp to boost it by a factor of four or five to around 2.5 V, which would have the additional benefit of lowering the impedance to work better with the Arduino’s ADC input circuitry. For now, I’ll pipe the voltage directly to an Arduino analog input:
SSAC10-11 PIR Sensor – breadboard
The linear Hall effect magnetic sensor and LM335 temperature sensor live just this side of the PIR can, sharing their VCC and ground connections in a most intimate manner. Remember, this is a breadboard, not a finished circuit… [grin]
The SSAC10-11 (if, indeed, that’s what it is) reports the voltage difference between a reference element shielded within the can and an active element exposed to incoming IR. The DC bias for that lashup produces 650 mV on the 47 kΩ source resistor (about 14 μA) and the internal arrangement produces a lower voltage (and thus current) when the exposed element sees a warmer object, which isn’t quite what I expected. Warming the can by direct finger contact produces an increasing voltage, due to heating the reference element and leaving the sensing element (relatively) cool, at least until conduction equalizes the elements.
I threw in a bit of averaging for each reading, not that it really matters:
#define PAVG 3
word ReadPIR(byte Pin) {
word Sense;
Sense = analogRead(Pin);
for (byte i = 1; i < PAVG; i++)
Sense += analogRead(Pin);
return Sense / PAVG;
}
The LED bargraph shows the current input as a single bar scaled between the minimum and maximum values, so that the display automatically adjusts to changing conditions. The boolean shift direction sends the bar upward on the breadboard LEDs as the PIR element sees warmer objects, which makes much more sense than showing the actual decreasing sensor voltage. The input generally rests in the green zone and both extremes show nice red bars:
In real life, you’d want a reset button, or some code that gradually drifts the extrema toward the running average of the input, so they’re not stuck forever.
Updating the displays every 100 ms seems about right. It’s crazy sensitive to anything within its field of view; sitting down two feet away is good for a few counts and a palm at 30 cm gives you 15 counts. As expected, the increases and decreases fade away exponentially over the course of a few tens of seconds.
If you wanted to do it right, you’d put a shutter or rotating aperture wheel in front, then track the AC signal difference between “scene” and “reference” views. A tiny Peltier module to stabilize the can temperature would make a lot of sense, too. Or, hey, that LM335 could report the actual can temperature, perhaps with everything embedded in a big thermal mass inside an insulating jacket with a peephole to the outside world. All that’s in the nature of fine tuning…
The Arduino source code:
// Nicera SSAC10-11 Single PIR Sensor
// Ed Nisley - KE4ANU - November 2012
//#include <stdio.h>
//#include <math.h>
//----------
// Pin assignments
const byte PIN_PIR = A2; // Passive IR sensor
const byte PIN_MOSI = 8; // data to shift reg
const byte PIN_SCK = 6; // shift clock to shift reg
const byte PIN_RCKB = 7; // latch clock for LED Bargraph
const byte PIN_RCKC = 12; // latch clock for LED character display
const byte PIN_HEARTBEAT = 13; // DO - Arduino LED
//----------
// Constants
const int UPDATEMS = 100; // update LEDs only this many ms apart
#define TCCRxB 0x02 // Timer prescaler
#define LED_SIZE 4 // chars per LED
#define LED_DISPLAYS 1 // number of displays
#define LED_CHARS (LED_DISPLAYS * LED_SIZE)
union DL1414_ {
word ShiftWord; // word overlay
struct { // bitfield sent to the display
unsigned int Addr:2;
unsigned int NotWrite:1;
unsigned int Ctl3_7:5; // unused bits
unsigned int Data:7;
unsigned int Data7:1; // unused bit
} ShiftBits;
};
//----------
// Globals
int PIRBase, PIRSense, PIRMin, PIRMax, PIRRange, PIRDelta;
int PIRShift;
word LEDBits = 0x5555;
char LEDCharBuffer[LED_CHARS + 1] = "HELO"; // raw char buffer, can be used as a string
unsigned long MillisNow;
unsigned long MillisThen;
//-- Helper routine for printf()
int s_putc(char c, FILE *t) {
Serial.write(c);
}
//-- Send bits to LED bar driver register
void SetBarBits(word Pattern) {
shiftOut(PIN_MOSI,PIN_SCK,MSBFIRST,Pattern >> 8);
shiftOut(PIN_MOSI,PIN_SCK,MSBFIRST,Pattern & 0x00ff);
digitalWrite(PIN_RCKB,HIGH);
digitalWrite(PIN_RCKB,LOW);
}
void PulsePinHigh(byte PinID) {
digitalWrite(PinID,HIGH);
digitalWrite(PinID,LOW);
}
//-- Write single char to DL1414
void WriteLEDChar(char Char,char CharID) {
union DL1414_ DL1414;
DL1414.ShiftBits.Data = Char & 0x7F;
DL1414.ShiftBits.Addr = ~CharID & 0x03; // reverse order of chars
DL1414.ShiftBits.NotWrite = 1; // set up data and address
shiftOut(PIN_MOSI,PIN_SCK,MSBFIRST,DL1414.ShiftWord >> 8);
shiftOut(PIN_MOSI,PIN_SCK,MSBFIRST,DL1414.ShiftWord & 0x00ff);
PulsePinHigh(PIN_RCKC);
// delay(1000);
DL1414.ShiftBits.NotWrite = 0; // write the character
shiftOut(PIN_MOSI,PIN_SCK,MSBFIRST,DL1414.ShiftWord >> 8);
shiftOut(PIN_MOSI,PIN_SCK,MSBFIRST,DL1414.ShiftWord & 0x00ff);
digitalWrite(PIN_RCKC,HIGH);
PulsePinHigh(PIN_RCKC);
// delay(1000);
DL1414.ShiftBits.NotWrite = 1; // disable write
shiftOut(PIN_MOSI,PIN_SCK,MSBFIRST,DL1414.ShiftWord >> 8);
shiftOut(PIN_MOSI,PIN_SCK,MSBFIRST,DL1414.ShiftWord & 0x00ff);
PulsePinHigh(PIN_RCKC);
// delay(1000);
}
void WriteLEDString(char *pString) {
for (byte i=0; (i < LED_CHARS) && *pString; ++i)
WriteLEDChar(*pString++,i);
return;
}
//-- Sample PIR with a dab of averaging
#define PAVG 3
word ReadPIR(byte Pin) {
word Sense;
Sense = analogRead(Pin);
for (byte i = 1; i < PAVG; i++)
Sense += analogRead(Pin);
return Sense / PAVG;
}
//------------------
// Set things up
void setup() {
pinMode(PIN_HEARTBEAT,OUTPUT);
digitalWrite(PIN_HEARTBEAT,LOW); // show we arrived
// TCCR1B = TCCRxB; // set frequency for PWM 9 & 10
// TCCR2B = TCCRxB; // set frequency for PWM 3 & 11
pinMode(PIN_MOSI,OUTPUT);
digitalWrite(PIN_MOSI,LOW);
pinMode(PIN_SCK,OUTPUT);
digitalWrite(PIN_SCK,LOW);
pinMode(PIN_RCKB,OUTPUT);
digitalWrite(PIN_RCKB,LOW);
pinMode(PIN_RCKC,OUTPUT);
digitalWrite(PIN_RCKB,LOW);
Serial.begin(9600);
fdevopen(&s_putc,0); // set up serial output for printf()
printf("Passive IR sensor - SSAC10-11\r\nEd Nisley - KE4ZNU - November 2012\r\n");
WriteLEDString(LEDCharBuffer);
SetBarBits(LEDBits);
PIRBase = ReadPIR(PIN_PIR);
PIRMin = PIRBase - 5;
PIRMax = PIRBase + 5;
PIRRange = PIRMax - PIRMin;
printf("Passive IR base: %d\n",PIRBase);
delay(1000);
MillisThen = millis();
}
//------------------
// Run the test loop
void loop() {
MillisNow = millis();
if ((MillisNow - MillisThen) > UPDATEMS) {
digitalWrite(PIN_HEARTBEAT,HIGH);
PIRSense = ReadPIR(PIN_PIR);
PIRDelta = PIRSense - PIRMin;
PIRMin = min(PIRMin,PIRSense);
PIRMax = max(PIRMax,PIRSense);
PIRRange = PIRMax - PIRMin;
// printf("PIR: %d Min: %d Max: %d Range: %d Delta: %d\n",
// PIRSense,PIRMin,PIRMax,PIRRange,PIRDelta);
PIRShift = (9 * PIRDelta)/PIRRange;
LEDBits = 0x00001 << PIRShift;
SetBarBits(LEDBits);
sprintf(LEDCharBuffer,"%4d",PIRSense);
WriteLEDString(LEDCharBuffer);
digitalWrite(PIN_HEARTBEAT,LOW);
MillisThen = MillisNow;
}
}
Temperature seems an obvious thing to measure, so a bit of rummaging disgorged a classic LM335 temperature sensor that produce an output voltage directly calibrated in Kelvin at 10 mV/K: room temperature runs 296 K = 2.96 V. Nothing could be easier than this:
LM335 Temperature Sensor
The downside: a 1 °C temperature change corresponds to only 10 mV, which is barely two LSB of the Arduino ADC. In round numbers, a 1 °F change = 1 LSB, which doesn’t leave much room for measurement noise. I average five successive readings, which may be excessive, but the result seems stable enough:
For better accuracy, you must measure VCC on the Arduino board and plug that into the AVREF constant, because the ADC reference voltage comes from the power supply. If you’re powering the Arduino from a USB port, then don’t bother worrying about analog conversion accuracy, because VCC depends on which PC you use, the USB cable length, what load current you draw from the regulator, and probably the phase of the moon.
The magic number 100.0 converts 10 mV/K to K.
The four character DL1414 LED display works well enough for the kind of temperatures you might find around a human being and, if you have an LED bargraph display, you may as well throw that into the mix, too.
LM335 Temperature Sensor – 19 C
The bargraph has RRYYGGYYRR LEDs, so I scaled the temperature at 5 °C/bar and put 0 °C on the bottom of the display, which means 15-19 and 20-24 °C occupy the green bars in the middle. Fingertip temperatures light up the two yellow bars and body heat gets you into the red, so it’s a reasonable display. Just to show it works, here’s a closer look (0 °C is on the right, but you can reverse that easily enough):
LM335 Temperature Sensor – 25 C
The Arduino source code:
// LM335 Temperature sensor sensor
// Ed Nisley - KE4ANU - November 2012
//#include <stdio.h>
//#include <math.h>
//----------
// Pin assignments
const byte PIN_TEMPERATURE = A1; // Temperature sensor - LM335 = 10 mV/K
const byte PIN_MOSI = 8; // data to shift reg
const byte PIN_SCK = 6; // shift clock to shift reg
const byte PIN_RCKB = 7; // latch clock for LED Bargraph
const byte PIN_RCKC = 12; // latch clock for LED character display
const byte PIN_HEARTBEAT = 13; // DO - Arduino LED
//----------
// Constants
const int UPDATEMS = 1000; // update LEDs only this many ms apart
const float AVREF = 4.94; // Arduino analog reference
const float KTOC = -273.2; // Kelvin to Centigrade offset
const float BARSCALE = 5.0; // degrees per bar increment
#define TCCRxB 0x02 // Timer prescaler
#define LED_SIZE 4 // chars per LED
#define LED_DISPLAYS 1 // number of displays
#define LED_CHARS (LED_DISPLAYS * LED_SIZE)
union DL1414_ {
word ShiftWord; // word overlay
struct { // bitfield sent to the display
unsigned int Addr:2;
unsigned int NotWrite:1;
unsigned int Ctl3_7:5; // unused bits
unsigned int Data:7;
unsigned int Data7:1; // unused bit
} ShiftBits;
};
//----------
// Globals
int Temperature, BaseTemperature;
word LEDBits;
char LEDCharBuffer[LED_CHARS + 1] = "HELO"; // raw char buffer, can be used as a string
unsigned long MillisNow;
unsigned long MillisThen;
//-- Helper routine for printf()
int s_putc(char c, FILE *t) {
Serial.write(c);
}
//-- Send bits to LED bar driver register
void SetBarBits(word Pattern) {
shiftOut(PIN_MOSI,PIN_SCK,MSBFIRST,Pattern >> 8);
shiftOut(PIN_MOSI,PIN_SCK,MSBFIRST,Pattern & 0x00ff);
digitalWrite(PIN_RCKB,HIGH);
digitalWrite(PIN_RCKB,LOW);
}
void PulsePinHigh(byte PinID) {
digitalWrite(PinID,HIGH);
digitalWrite(PinID,LOW);
}
//-- Write single char to DL1414
void WriteLEDChar(char Char,char CharID) {
union DL1414_ DL1414;
DL1414.ShiftBits.Data = Char & 0x7F;
DL1414.ShiftBits.Addr = ~CharID & 0x03; // reverse order of chars
DL1414.ShiftBits.NotWrite = 1; // set up data and address
shiftOut(PIN_MOSI,PIN_SCK,MSBFIRST,DL1414.ShiftWord >> 8);
shiftOut(PIN_MOSI,PIN_SCK,MSBFIRST,DL1414.ShiftWord & 0x00ff);
PulsePinHigh(PIN_RCKC);
// delay(1000);
DL1414.ShiftBits.NotWrite = 0; // write the character
shiftOut(PIN_MOSI,PIN_SCK,MSBFIRST,DL1414.ShiftWord >> 8);
shiftOut(PIN_MOSI,PIN_SCK,MSBFIRST,DL1414.ShiftWord & 0x00ff);
digitalWrite(PIN_RCKC,HIGH);
PulsePinHigh(PIN_RCKC);
// delay(1000);
DL1414.ShiftBits.NotWrite = 1; // disable write
shiftOut(PIN_MOSI,PIN_SCK,MSBFIRST,DL1414.ShiftWord >> 8);
shiftOut(PIN_MOSI,PIN_SCK,MSBFIRST,DL1414.ShiftWord & 0x00ff);
PulsePinHigh(PIN_RCKC);
// delay(1000);
}
void WriteLEDString(char *pString) {
for (byte i=0; (i < LED_CHARS) && *pString; ++i)
WriteLEDChar(*pString++,i);
return;
}
//-- Sample temperature with a dab of averaging
#define TAVG 5
float ReadLM335(byte Pin) {
float Kelvin;
Kelvin = (float)analogRead(Pin);
for (byte i = 1; i < TAVG; i++)
Kelvin += (float)analogRead(Pin);
return Kelvin * (100.0 * AVREF) / (TAVG * 1024.0);
}
//------------------
// Set things up
void setup() {
pinMode(PIN_HEARTBEAT,OUTPUT);
digitalWrite(PIN_HEARTBEAT,LOW); // show we arrived
// TCCR1B = TCCRxB; // set frequency for PWM 9 & 10
// TCCR2B = TCCRxB; // set frequency for PWM 3 & 11
pinMode(PIN_MOSI,OUTPUT);
digitalWrite(PIN_MOSI,LOW);
pinMode(PIN_SCK,OUTPUT);
digitalWrite(PIN_SCK,LOW);
pinMode(PIN_RCKB,OUTPUT);
digitalWrite(PIN_RCKB,LOW);
pinMode(PIN_RCKC,OUTPUT);
digitalWrite(PIN_RCKB,LOW);
Serial.begin(9600);
fdevopen(&s_putc,0); // set up serial output for printf()
printf("Temperature sensor - LM335\r\nEd Nisley - KE4ZNU - November 2012\r\n");
BaseTemperature = KTOC + ReadLM335(PIN_TEMPERATURE);
WriteLEDString(LEDCharBuffer);
LEDBits = 0x5555;
SetBarBits(LEDBits);
printf("Base Temperature: %d C\n",(int)BaseTemperature);
delay(1000);
MillisThen = millis();
}
//------------------
// Run the test loop
void loop() {
MillisNow = millis();
if ((MillisNow - MillisThen) > UPDATEMS) {
digitalWrite(PIN_HEARTBEAT,HIGH);
Temperature = KTOC + ReadLM335(PIN_TEMPERATURE);
printf("Temperature: %d C\n",(int)Temperature);
LEDBits = 0x0200 >> (1 + (int)(Temperature/BARSCALE)); // move upward on display!
SetBarBits(LEDBits);
sprintf(LEDCharBuffer,"%-3dC",(int)Temperature);
WriteLEDString(LEDCharBuffer);
digitalWrite(PIN_HEARTBEAT,LOW);
MillisThen = MillisNow;
}
}
The Smell of Molten Projects in the Morning 