The (not really) official electronics workbench thread


Mr_Roboto

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Although a computer nerd by profession, by education I was into electronics back in the day.After a long, winding diversionary road I think it would be fun to start returning to some of that as a hobby. To that end I've been investing.



This is my latest purchase, it's a 50mhz Tek scope. I paid $100 with 2 good 10X probes, a 100X probe and a broken 10X probe. In retrospect Ebay had 200mhz ones for about $50-75 more shipped but I don't think I did terrible.



This is an RF Probe I made using a scrap PCB and misc components I had laying around. The idea is you take RF energy and rectify it so you can tune radios and stuff like that. With the O-scope it's probably less relevant than it used to be but could still come in handy for "peaking" stuff. Missing on it is the alligator clip to connect ground to the device in testing.



My Simpson 260s, DVM and Hakko soldering station. I replaced my Weller TC-202 this year with it (great if you find one cheap, last one was $10 and lasted me a decade plus of heavy use) and can't be happier. The beater Simpson on the left is one I've had forever and it broke. Naturally after I bought the one on the right I got it fixed up. I stole the one on the right for a princely sum of $15 and it's hella clean.



This is my latest project, an Eico 324 RF Signal generator. It is something I've had for a long time, and when I looked at the wave form on it there was horrible distortion. Although it's far from perfect now, I found out that the potentiometer for the RF Fine had a short in it. Modulation I'm not sure about but I'm going to continue to work on that. I may even have some of the right knobs to put back on it. Looking to upgrade but hoping this gets me past the hump.

What I'm wanting to do in the future gear wise is get a decent frequency counter, a better signal generator, a computer to drive my EPROM programmer (not pictured) and if I can find a smoking hot deal get a service monitor (dubious for the coin I'm willing to spend.)

The projects I'm wanting to work on in the near future are get some ham gear fixed up (I need to build a PSU for my HW-101 or get one for it and some commercial radios I'd like to rework) a PIC Micro project or two possibly, some tube audio amps (I have a design or two on deck I never built) and lastly build a WWV receiver which was a class project I never got working, probably trying for a tube amp here too although hybrid isn't totally out of the question by any means. Car wise I'd love to build a budget focused 4L80E controller that would be in the Megashift or less price point. Sure some stuff will get added to that, but it's more than a good start.

Any other electronics geeks here? If so post what you're up to or your bench.
 

TonzKnock-G

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Use it or lose it and I definitely lost it. Lol. Brings me back to devry days.
 
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Mr_Roboto

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Use it or lose it and I definitely lost it. Lol. Brings me back to devry days.
I was having trouble recalling how to calculate power based off resistance a few weeks back. Racking my brain on it getting more and more pissed off.

de draaggolf ~~~~~: Penning Down a Crystal

A version of this is on the docket for tonight I Think.

That trans controller looks wicked awesome. I didn't get into detail on it but controlling a 4L80 shouldn't be that difficult. (I was in the planning phases of a very similar project.)
 
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Mr_Roboto

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Okay, first circuit is the one previously mentioned. Parts are a crystal, 2.2M Ohm resistor, a 1K resistor (I used a 330 ohm resistor, no issues) a couple of 12PF capacitors (I used 15) and a 1/2 of a 74HCT00 quad dual input NAND gate.

Gate Datasheet:
http://www.nxp.com/documents/data_sheet/74HC_HCT00.pdf

Actual Circuit:



Built Circuit:



I think the breadboard sat in the garage for several years or something, but it still gets the job done. As you can see there's about half a dozen parts.



This is the lowest frequency crystal I tried, around 1.686mhz. Taking the period based on guestimation of the scope and inverting it got me right on the money.



another shot of the same wave form. As the frequency went up (I tested to ~16 mhz crystals) The waveform definitely got more and more round as time went by, I don't know if there may be aspects of my probe that caused it or if slew of the IC did. I certainly lean towards slew based on the initial waveforms even at lower frequencies.

I also dug out some of my 10mhz crystals that I want to use for my WWV receiver, 7 pin vacuum tube style. Hoping I can pull them enough to use em with an IF.
 

nytebyte

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$100 for an O-scope, damn.

I really need one at work, but never could justify the expense. Never thought about getting a used one, but it's a great idea.
 

OffshoreDrilling

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this thread is relevant to my interests.

I don't get to tinker with stuff terribly often. Most of my experience is with power electronics. Deal a lot with IGBTs, SCRs,SSRs, rectifiers. Not terribly knowledgeable, self taught and just enough to be able to troubleshoot the stuff I work on (variable frequency drives, some basic heating process control stuff)
 

OffshoreDrilling

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$100 for an O-scope, damn.

I really need one at work, but never could justify the expense. Never thought about getting a used one, but it's a great idea.
They're relatively cheap, even new, depending on what you need. A brand new Rigol can be had sub $400

I see old tectonix CRT screened ones going out into the trash all the time at work.
 
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Mr_Roboto

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this thread is relevant to my interests.

I don't get to tinker with stuff terribly often. Most of my experience is with power electronics. Deal a lot with IGBTs, SCRs,SSRs, rectifiers. Not terribly knowledgeable, self taught and just enough to be able to troubleshoot the stuff I work on (variable frequency drives, some basic heating process control stuff)
There were a lot of things I got on my own before I started doing school for it, but I will say I hit road blocks inevitably especially around things like angular velocity and phasors. My math wasn't up to the skill I needed to actually understand what was happening. I will say that if you have better trig than I did you could probably book most of it out and if not find the rest on youtube these days.

They're relatively cheap, even new, depending on what you need. A brand new Rigol can be had sub $400

I see old tectonix CRT screened ones going out into the trash all the time at work.

In for trashed scopes.

$100 for an O-scope, damn.

I really need one at work, but never could justify the expense. Never thought about getting a used one, but it's a great idea.

The Tek 475 go for udner 200 shipped on ebay it seems, and they're 200mhz vs the 50mhz of this one. I'm thinking about seeing what I'd have to interchange to bump mine to a 200mhz unit. There are also some pretty decent looking PC units you can get for that range too.

Any of you folks cut boards? Probably wanting to go that route at some point. It seems like a lot of the through mount stuff that existed in the past doesn't any more, so SMT is the way of the future. There's tons of documentation out there about home made etching solutions, figure I'll try to dig some scraps out and try em.
 
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Mr_Roboto

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Haven't gotten much done with the holidays, just goofing around. Something I'm messing with is how to determine the inductance of coils which is kind of a mystery in a lot of cases. Here's my technique so far:

-Put inductor in series with known resistance value using a signal generator at a known voltage and frequency level. This creates a voltage divider circuit I can get the inductive reactance from. I ended up using a carbon resistor because the metal film one was giving odd noise at RF frequencies.
-Take readings and do some math on them (below.)
223 ohms for resistance
XL is a mystery we are solving for
1.7V across L which means 1.5V across R
.05uSX1.32 boxes for period (to calc freq, xtal was 16 mhz) Instrumentation is too crude to really get a good idea of time, so this is more of a sanity check.)

-1.(1/.05*1.32)=15,151,515.1515hz or about 7% low which is likely rounding error. I'll just use 16, I trust the crystal more than my scope and eyesight.

E=IR or
1.5V=223I or
1.5v/223=I=0.0067264573991A

I remains constant across a series circuit, so all we have to do is flip some stuff around:

1.7=XL*0.0067264573991 or
XL=1.7/0.0067264573991=252.733333333

To figure the actual inductance we use:
XL=2piFL or
243=2pi(16,000,000)L
243/(2*pi*16,000,000)=L=2.4171677399e-06 or 2.417 uH at 16 mhz.

This XL can vary depending on frequency as well since it's wound on an iron core. Typically my recommendation would be calculate XL at the frequency you're running at for non-air coils.

The other thing I'll say is that you should be able to use a similar formula for capacitors as well (notably varaibles of a mystery value) but substitute in XC=1/2piFC for the reactance formula.

Also, bought some new toys off ebay. Should be here in a month or so ;P

DDS AD9850 Signal Generator Module Signal Sine Square Wave 0-40MHz | eBay

This is a Direct Digital Synthesizer. This little board should have about 0-60mhz output, and is digitally controlled. Debating if I want to use a PIC or a Raspberry Pi to control it. Some people are even using these for FM synthesis so that's a cool option later on I may be able to use on 10M or 6M ham with a bit of work.

New PLJ-8LED-H RF Signal Frequency Counter Cymometer Tester Module 0.1~1000MHz | eBay

This is a frequency counter. I am going to end up getting a nice bench unit for $10 I will likely end up mounting it on my HW-101 as a readout on the VFO ultimately.
 

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I mess around with some electronics from time to time. I did a lot of robotics in high school and still mess with it now. The new cheap-ish LIDAR sensors are kind of re-piquing my interest in robotics...SLAM is pretty interesting stuff. That, and all the badass new computers and controllers out there now...The r pi, arduino, up board, etc.

I've also dabbled in some hardware hacking of various IOT/embedded devices. SOHO routers, IP cameras, etc. Soldering in header pins on the UART pads, connecting with an FTDI conveter, getting root access or dumping the eeprom memory, etc. Haven't gotten too far into it though. I've been wanting to get something like a GoodFET so I can take it to the next level and start doing stuff with JTAG.

edit: And I'm going to take the Ham licensing exam next weekend, which is quickly opening a whole new bag of worms.
 

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My first MCU. Got it in 7th grade for Christmas(~2001) I believe:




Testing out a Maxbotix Sonar module with an Arduino Uno:




Some parts for a fire-fighting robot I've yet to build. Continuous-rotation servos, (3)Maxbotix sonar modules, DFrobot Flame Detector, Pololu QTR-1A Reflectance Sensors(floor/edge detection), Axon II MCU:

 
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Mr_Roboto

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I mess around with some electronics from time to time. I did a lot of robotics in high school and still mess with it now. The new cheap-ish LIDAR sensors are kind of re-piquing my interest in robotics...SLAM is pretty interesting stuff. That, and all the badass new computers and controllers out there now...The r pi, arduino, up board, etc.

I've also dabbled in some hardware hacking of various IOT/embedded devices. SOHO routers, IP cameras, etc. Soldering in header pins on the UART pads, connecting with an FTDI conveter, getting root access or dumping the eeprom memory, etc. Haven't gotten too far into it though. I've been wanting to get something like a GoodFET so I can take it to the next level and start doing stuff with JTAG.

edit: And I'm going to take the Ham licensing exam next weekend, which is quickly opening a whole new bag of worms.
Cool, I did it a long time ago pretty well to get transmit rights for stuff I built. It's a lot of fun regardless. I have very minimal gear up although I think that's going to change in the future.

I never actually got into the robotics, although I wish I did. It looks fun, and there's a lot of room for development there that can be slanted a lot of directions like automotive these days.

In terms of the hacking stuff, There's been a few ham radio hacks around dumping firmware. I think that will be the future at some level, there are 3 digital modes right now and they're all trying to force people into running their stuff. A third party firmware that let a person run all of them on the same radio(s) would open a lot of doors quite frankly.

Now then, since I'm wanting to do stuff with hollow state (tube) systems, I'm going to want a power supply to mess around with. Keep in mind this isn't for high power duty, and that I'll build another PSU up for that if/when the time comes.



To answer your question, yes I have a thing for PC PSUs as project chassis. They're dirt easy to salvage, a good size for a lot of stuff and the PCBs of the PC PSU provides a nice source of misc. components.



The hole was cut using a Dremel. First time I've ever done it, and though the wheels cut aggressively they have virtually zero lifespan and are practically like glass. Overall I'm not surprised they give you 3 dozen of em for under $5.

I need a grommet and terminal strip for the outside now, unless I decide to do power another way. Doubt it though.

Current plans are a full wave bridge, a couple of large uF capacitors and leaving it at that. What else is nice about this setup is it has a full set of Filament center taps (5,6.3,12V) so I don't have to worry about any weirdness around that.
 
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Mr_Roboto

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Something I forgot in the last post was how I figured out the hole. I ended up marking it out based on my calipers, hating that/getting it less than right so I subsequently made a cardboard template and using that to drill/cut.



Bit more work tonight:



Added some diodes and the AC wiring first. Notice the grommet I added too. Menards had em of all places, so I have a few extra now. Always a good thing to have. It's full wave rectification, the reason I can get away with 2 diodes instead of a full 4 diode bridge is I'm running the center tap to ground.



This is the other side of the AC wiring. Behind the switch where you can't really see it is the socket for a standard PC power cord. Why reinvent the wheel and strain relief is gtg. Fuse is 1A, could probably go down to half that and be safe but it's what I had and may get changed later. Both of which are quite honestly add ons I didn't put in the original design.



I added a 220 UF capacitor before the 4.5H Choke, and a 330 after. Another last minute addition here is the 100K resistor to ground from the positive rail. I decided I didn't need to leave the caps in a permanent state of charge to shock the living hell out of me at some random point. They still take quite some time to bleed down.



Lastly, a schematic of my supply. Really simple, brute force iron based PSU. No switchers here. Maybe another day.

I may add a meter to this, not 100% either way yet. I'm at least wanting some sort of indicator that the capacitors have discharged fully. I've been shocked by tube amps before, so I'd rather not take chances.
 
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Mr_Roboto

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Well, been messing around cursing a lot etc. and finally have oscillations.

For some reason I have a few oscillations. This one is at a few hundred khz. Not sure what's up here, probably parasitic.





These are what I believe to be the "good" oscillations. I need a frequency counter to be sure, but hopefully we'll find out soon.

This is what I believe to be the "good" oscillations. Circuit is likely way high on voltage now and didn't want to bias well (I have about 1.2M of grid leak resistor in it, which seems odd based on most of the circuits that use 100K) but that may change as I increase the plate resistor. B+ is way higher than the transformer is rated to, not sure what's going on there. It may be that I'm getting closer to peak voltage due to the capacitance in the circuit and running off 120ish volts vs 110. Not 100% at this time. Probably going to have to build/use a regulation circuit at some point to drop it down. The plate in the tube is still a bit cherry so less voltage would probably be a good thing. I am at ~5W I think and the triode section is rated to about half of that.
 

b00sted

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I've personally wanted to build a rail-gun for yeeeears.
 
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Mr_Roboto

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I've personally wanted to build a rail-gun for yeeeears.
We need more capacitors. Ever seen a quarter shrinker? In my dreams perhaps one day.
 

b00sted

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We need more capacitors. Ever seen a quarter shrinker? In my dreams perhaps one day.

I need to start looking around for those massive capacitors so I can do stuff like a rail gun or a can crusher.
 
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Mr_Roboto

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Id love to build a megasquirt kit and do a swap just to sort of prove i can even though after buying my 5.0 i have no need to now.
Do the megasquirt avoid the gpio/megashift like the plague.
 

Sprayin

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I built a Megasquirt like 8 years ago and its still just sitting in a box. Never put it in a car.
 

BADAZZTEALCOBRA

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Do you have any use for ESD mats? We're going to be changing out some here at my work and if you don't mind older ones that are a little beat up or might need to be cut down to fit you would be more than welcome to them?
 

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