DSO150: USB Serial Output

Taking all those pictures of the DSO150 screen reminded me it has a data dump function: press the V/Div and ADJ buttons to squirt configuration, measurements, and trace data from the TX pad on the main board, just in front of the red-black power wires hot-melt glued in place:

DSO150 USB serial adapter - interior
DSO150 USB serial adapter – interior

The picture shows the “before” stage, while I was figuring out where to carve another hole in the case.

NB: The 113-15001-111 DSO150 firmware version includes the serial output option, so you won’t need third-party firmware. Similarly, current PCBs bring the serial pins to neatly labeled header pads. You should refer to the JYETech DSO150 / DSO Shell product page for the details.

After all the cuttin’ and filin’ was done, it looked like this:

DSO150 USB serial adapter - exterior
DSO150 USB serial adapter – exterior

The power switch on the back of the case (top of the picture) disconnects the lithium cell from the charge controller board (now tucked behind the battery) to eliminate any trickle current discharge. Charging the battery thus requires turning that switch on and turning the scope off with its own power switch (along its front edge). Capturing trace data requires having both switches on (duh), whereupon the scope’s normal operating current convinces the charge controller that the cell hasn’t reached full charge. Turn the scope off and, most likely, the controller will tell you the cell is fully charged.

An intro blurb squirts from the port at 115200 in good old 8N1 format when you turn the scope on:

DSO Shell
JYE Tech Ltd.
WWW.JYETECH.COM
FW: 113-15001-111

Pressing the V/Div and ADJ buttons dumps the trace data:

VSen,0.5V
Couple,DC
VPos, -2.02V
Timebase,0.2s
HPos,00362
TriggerMode,NORM
TriggerSlope,Rising
TriggerLevel,  2.02V
RecordLength,01024
Vmax,  2.85V
Vmin,  0.24V
Vavr,  0.87V
Vpp,  2.61V
Vrms,  1.03V
Freq, 0.441Hz
Cycl, 2.266s
PW, 0.231s
Duty, 10.2 %
SampleInterval,00008ms
00000,0000000000, 0.8518688
00001,0000000008, 0.5273474
00002,0000000016, 0.5273474
00003,0000000024, 0.5476300
00004,0000000032, 0.5476300
00005,0000000040, 0.5476300
<< snippage >>
01015,0000008120, 0.8113037
01016,0000008128, 0.8315863
01017,0000008136, 0.8315863
01018,0000008144, 0.8315863
01019,0000008152, 0.8315863
01020,0000008160, 0.8315863
01021,0000008168, 0.8315863
01022,0000008176, 0.8518688
01023,0000008184, 0.8518688

It’s all in neatly comma-separated-value format, so you can slam it into a spreadsheet and have your way with it. Utilities also exist to capture the data, extract the values, and send them directly to GNUplot, etc.

Like so:

DSO150 test image
DSO150 test image

If I expected to do a lot of that, I’d boldify the traces and embiggen the text, all of which is in the nature of fine tuning.

It’s hard to reproduce the beauty of the DSO150’s display, though:

DSO150 test image
DSO150 test image

The DSO150 remains pretty good for being the worst oscilloscope I’m willing to use …

Tour Easy: Baofeng Radio PTT Cable Glitch

The signal from the Baofeng UV-5R HT tucked behind the seat of my Tour Easy became exceedingly choppy on recent rides. Here’s an earlier version to give you an idea of the situation:

Radio in seat wedge pack in bottle holder
Radio in seat wedge pack in bottle holder

Of course, it worked perfectly in the garage and only failed while on a ride. The clue turned out to be having it fail more on rough roads and crappy scab patches (courtesy of NSYDOT) than on relatively smooth asphalt.

That led me to wiggle of All The Cables while crouched beside the bike in the garage, listening to another HT, and watching the transmit LED. After about five minutes of this, I found wiggling the 3.5 mm connector between the cable from the PTT button on the handlebar and the radio blinked the transmit LED: ah-HA!

The connector had worked itself loose from the straps holding the radio pack in place, pulled some slack in the cable, and was bouncing around in mid-air. A wrap of duct tape now holds the connector halves together, the upper loop passes around the Velco-ish strap, and the lower loop (from the PTT button) goes through the bottom of the repurposed bottle holder:

Tour Easy - Baofeng PTT cable connection
Tour Easy – Baofeng PTT cable connection

No trouble on the next two rides, so we’ll call it fixed.

Protip: it’s always the connector.

Baofeng Bike Helmet Headset Wiring Repair

The audio output wire from the Baofeng UV-5R to my bike helmet headset adapter broke after a year and a half, far longer than I expected:

Baofeng - broken spkr wire
Baofeng – broken spkr wire

It’s the green one, over on the left, pulled out of the heatstink tubing that should have provided some strain relief, having broken at the solder joint to the resistor.

A quick & easy fix, after which I reapplied even more tape to hold everything in place.

Maybe it’ll last two years this time around …

Tektronix Circuit Computer: Layout Analysis

Following a linkie I can no longer find led me to retrieve the Tektronix Circuit Computer in my Box o’ Slide Rules:

Tektronix Circuit Computer - front
Tektronix Circuit Computer – front

I’m pretty sure it came from Mad Phil’s collection. One can line up the discolored parts of the decks under their cutout windows to restore it to its previous alignment; most likely it sat at the end of a row of books (remember books?) on his reference shelf.

The reverse side lists the equations it can solve, plus pictorial help for the puzzled:

Tektronix Circuit Computer - rear
Tektronix Circuit Computer – rear

Some searching reveals the original version had three aluminum disks, shaped and milled and photo-printed, with a honkin’ hex nut holding the cursor in place. The one I have seems like laser-printed card stock between plastic laminating film; they don’t make ’em like that any more, either.

TEK PN 003-023 (the paper edition) runs about thirty bucks (modulo the occasional outlier) on eBay, so we’re not dealing in priceless antiquity here. The manual is readily available as a PDF, with photos in the back.

Some doodling produced key measurements:

Tektronix Circuit Computer - angle layout
Tektronix Circuit Computer – angle layout

All the dimensions are hard inches, of course.

Each log decade spans 18°, with the Inductive Frequency scale at 36° for the square root required to calculate circuit resonance.

Generating the log scales requires handling all possible combinations of:

  • Scales increase clockwise
  • Scales increase counterclockwise
  • Ticks point outward
  • Ticks point inward
  • Text reads from center
  • Text reads from rim

I used the 1×100 tick on the outer scale of each deck as the 0° reference for the other scales on that deck. The 0° tick appears at the far right of plots & engravings & suchlike.

The L/R Time Constant (tau = τ) pointer on the top deck and the corresponding τL scale on the bottom deck has (what seems like) an arbitrary -150° offset from the 0° reference.

The Inductive Frequency scale has an offset of 2π, the log of which is 0.79818 = 14.37°.

The risetime calculations have a factor of 2.197, offsetting those pointers from their corresponding τ pointer by 0.342 = log(2.197) = 6.15°.

A fair bit of effort produced a GCMC program creating a full-size check plot of the bottom deck on the MPCNC:

Tektronix Circuit Computer - Bottom Deck - scale check plot
Tektronix Circuit Computer – Bottom Deck – scale check plot

By the conservation of perversity, the image is rotated 90° to put the 1 H tick straight up.

The 3018 can’t handle a 7.75 inch = 196 mm disk, but a CD-size (120 mm OD) engraving came out OK on white plastic filled with black crayon:

Tek CC bottom - ABS 160g 2400mm-min
Tek CC bottom – ABS 160g 2400mm-min

The millimeter scale over on the right shows the letters stand a bit under 1 mm tall. And, yes, the middle scale should read upside-down.

Properly filling the engraved lines remains an ongoing experiment. More downforce on the diamond or more passes through the G-Code should produce deeper trenches, perhaps with correspondingly higher ridges along the sides. Sanding & polishing the plastic without removing the ink seems tedious.

The Great Dragorn of Kismet observes I have a gift for picking projects at the cutting edge of consumer demand.

More doodles while figuring the GCMC code produced a summary of the scale offsets:

Tektronix Circuit Computer - scale angle tabulation
Tektronix Circuit Computer – scale angle tabulation

Musings on the parameters of each scale:

Tektronix Circuit Computer - scale parameters
Tektronix Circuit Computer – scale parameters

How to draw decades of tick marks:

Tektronix Circuit Computer - decade tick doodles
Tektronix Circuit Computer – decade tick doodles

It turned out easier to build vectors of tick mark values and their corresponding lengths, with another list of ticks to be labeled, than to figure out how to automate those values.

More on all this to come …

Tour Easy: PTT Switch Replacement

The PTT switch on Mary’s Tour Easy became intermittent:

Tour Easy - failed PTT switch
Tour Easy – failed PTT switch

It’s been sitting there for least five years, as witnessed by the sun-yellowed hot melt glue blob, which is pretty good service from a switch intended for indoor use. The 3D printed button never fell off and, in fact, was difficult to remove, so that worked well.

I took it apart and cleaned the contacts, but to no avail, so her bike now sports a new switch with a similar rounded dome:

Tour Easy - new PTT switch
Tour Easy – new PTT switch

I clipped the wires a bit beyond the terminals and soldered the new switch in place, so it’s the same cable as before.

Now, to see how long this one lasts …

Baofeng UV-5R Squelch Settings

The Baofeng UV-5R radios on our bikes seem absurdly sensitive to intermodulation interference, particularly on rides across the Walkway Over the Hudson, which has a glorious view of the repeaters and paging transmitters atop Illinois Mountain:

Walkway Over The Hudson - Illinois Mountain Antennas
Walkway Over The Hudson – Illinois Mountain Antennas

A better view of the assortment on the right:

Illinois Mountain - North Antennas
Illinois Mountain – North Antennas

And on the left:

Illinois Mountain - South Antennas
Illinois Mountain – South Antennas

Not shown: the Sheriff’s Office transmitter behind us on the left and the Vassar Brothers Hospital / MidHudson pagers on either side at eye level. There’s plenty of RFI boresighted on the Walkway.

Anyhow, none of the Baofeng squelch settings had any effect, which turned out to be a known problem. The default range VHF covered a whopping 6 dB and the UHF wasn’t much better at 18 dB, both at very low RF power levels.

We use the radios in simplex mode, generally within line of sight, so I changed the Service Settings to get really aggressive squelch:

Baofeng UV-5R - Improved Squelch Settings
Baofeng UV-5R – Improved Squelch Settings

I have no way to calibrate the new signal levels, but I’d previously cranked the squelch up to 9 (it doesn’t go any higher) and, left unchanged, the new level makes all the previous interference Go Away™. Another ride over the Walkway with the squelch set to 4 also passed in blissful silence.

If the BF-F9 levels mean anything on a UV-5R, that’s about -100 dBm, 20 dB over the previous -120 dBm at squelch = 9.

The new squelch levels may be too tight for any other use, which doesn’t matter for these radios. As of now, our rides are quiet.

[Update: Setting the squelch to 5 may be necessary for the Walkway, as we both heard a few squawks and bleeps while riding eastbound on a Monday afternoon. ]