Reddit:Electronics

There's not a lot of love for the JT these days. Nevertheless they crossed my mind the other day and I couldn't help but put one together. I was as always amused by their ability to drive an led from incredibly low voltage. I had it down to 0.39V at one point.

The age old issues cropped up immediately when I wanted to make an led last on a button cell for a long time. They're great at pulling out some juice at low voltages, but not so good when the cell is brand new. Which is a shame. If one of these could take advantage of all the power in a button cell, they'd last much much longer obv.

There's all kinds of regulated varieties on the internet. Most of them rely on negative feedback at the cost of high base (or drive) current. In many cases, the amount of power being consumed by the base circuit was using more power than the led itself. This is primarily due to using a low value resistor into the base of a bjt. To regulate the power (often voltage), a second transistor diverts some of the current to ground. As power consumption grows, more base current is diverted until these balance out over the range of input voltages.

If the drive current and positive feedback could be controlled without wasting most of it, a ton of power could be saved. So I came up with this; a jfet between L2 and the base resistor. Instead of diverting current in the bias circuit to ground, it is directly regulated with a variable "resistance."

Of course to control the jfet would require a floating negative voltage that was proportional to the power being consumed by the boost circuit. So I added an additional winding, L3, to provide an isolated supply that would rise and fall with the rest of the joule thief. Then it was a simple matter of using a low power (low Vf diodes and small ceramic caps) rectifier with a pot to dial in the control voltage.

Jfets have an incredibly high impedance, and I used a 2 megaohm pot so the control circuit utilizes very little power.

Anyway I've been rambling. I thought the idea was neat and now I have a working version to see how long it lasts.

If anyone is interested, I can post a schematic. This is nothing special, but a fun detour from the actual projects I've been working on.

My spine hurts all over. 201 leds are smaller than a grain of salt! Even harder to solder on a home made pcb! Plus all the time troubleshooting broken tracks and drilling holes by hand. Those blobs kf solder you see are vias that link the rear and front copper tracks together. Did I mention my spine hurts?

“The use of WD-40 Specialist Contact Cleaner may result in damage to the laptop motherboard and is therefore not recommended for such applications.”

This i my workbench in the basement. Really happy with the layout and space. MIssing basically nothing more than a real heating system. At the moment working on a testjig for a pcb

This bench of mine has served me well for many projects including fixing a lot of things for family and friends. My current project is fixing that vacuum tube oscilloscope in the 5th picture. I’m also currently rearranging my drawer layout so things are still half labeled at the moment.

A rare kot of vintage military-grade circuit boards originating from Cold War-era radar infrastructure, consistent with systems such as PAVE PAWS. These boards represent a time when electronics were engineered for absolute reliability under mission-critical conditions. Each unit features meticulously arranged multi-channel circuitry, shielded modules, precision-tuned components, and electromechanical relays — all indicative of early high-performance signal processing design. The construction alone tells the story: hand-calibrated elements, gold-edge connectors, and robust analog architecture built to operate continuously in high-stakes environments. This is not consumer hardware. It is a preserved fragment of early warning defense technology — a physical artifact from an era defined by vigilance and engineering excellence. Ideal for: • Advanced collectors of military or Cold War technology • Display in studios, offices, or curated spaces • Engineers and historians of early electronic systems Condition: Untested. Original vintage condition with visible signs of age consistent with long-term storage. Available Serious only

Pictured is the offender, my custom 84V 480A brushed DC motor driver. While testing, I had to make some adjustments to the rev1 routing, since apparently I forgot to run DRC before sending it to the fab. Tried to change the logic power supply to the FET drivers from 12V to 5V, forgot to cut one trace, and ended up bridging 5V to 12V. I used a lead acid battery instead of a current limited power supply for testing, connected it to my laptop without a USB isolator, and... well, I no longer have a laptop.

I wonder how I'll explain to my professors why I won't be able to submit my paper draft that is due tonight.

About Chua's citcut:
https://www2.eecs.berkeley.edu/Pubs/TechRpts/2009/EECS-2009-20.pdf

My implementation:
CHUA custom PCB board (thank you, JLCPCB!), TL082 op amps
signal conditioner board (from +/-6V to 0 - 2V, from +/-1V to 0-2V)
X/Y simple scope - Teensy4.0+ ILI9341 SPI display.

Video: https://imgur.com/a/R0H5TSl

Just some quick soldering in my free time. Wanted to see if its possible to bodge a 50 Ohms dummy load. Its not perfect since it picks up a lot of noise without any EMF shield and the impedance is not exactly 50 Ohms with these resistors.

So the design is ready and working in LTSpice.

The red graph shows the voltage of the L3L4 transformer, that can be seen in the middle of the circuit. The voltage oscillates roughly between +10 and -10 kV.

The blue graph shows the voltage difference between the upper and lower CW circuits output.

Was tinkering this rainy weekend, initially just playing around with assessing noise performance of a couple of amps, which quickly reminded me about input offset at higher gain. Using a pack of 8x fresh AA cells for most of these measurements, in an inverting amp with gain of 101 (5% error possible). The low-voltage amps were tested with 3x fresh AA cells, just under 5V.

The homebrew op amp is made from non-sorted 2N3904/2N3906, circuit from Figure 2 of https://sound-au.com/project07.htm

The vintage part numbers were generally vintage mid-1970s to late-1980s. Only a single amplifier was measured in every case.

Nothing too rigorous but amusing to see how well they general conformed to datasheet typical. Pleasantly surprised how good the modern ST variant of the LM324A is. Just sharing in case anyone else finds it interesting.

I found it cheaper to buy lower amperage power supplies and having them in parallel instead of one with the same specs. I have made a passive balancer using 0.05 ohm resistors and one fuse so that one power supply doesn't works more than the rest. I am going to add ideal diodes to make it diode OR'ing to even further make the balancing better. Using this to drive a flyback transformer. The power supplies are 24V 6A so all four gives me 24V 24A.

Poor little bugger.

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This is my project: ZVS feeding a transformer feeding a symmetrical Cockroft-Walton voltage multiplier. The circuit in the pic is the second part, earlier i posted the CW diagram that i designed with falstad.

I study electrical engineering, and i decided to challenge myself with building this setup. The voltage between the 2 multipliers will be 240kV and produce ~30cm arcs(30cm according to gemini).

I had problems with this ZVS and LTSpice, the simulation was harder to get going than the actual circuit, but today i succeeded with it. I think i'll reward myself with some ice cream later! :)

I’ve been working on a custom CH32V006 dev board for OpenServoCore, which is my attempt to turn cheap servos like the MG90S into smart actuators with Dynamixel-style single-wire UART. PCBWay kindly sponsored the fabrication and assembly for this first spin.

When the boards arrived, I plugged one in over USB-C and immediately noticed the 3.3V rail LED was off. Measuring the rail gave me 0.84V. I checked all 5 boards and got the same result every time, so it was pretty clear this was not a one-off assembly issue. I even injected an external 3.3V supply directly onto the rail and it was still stuck at 0.84V. At that point the evidence was clearly pointing to my design, not the fab.

After staring at the KiCad files and schematics for way too long and finding nothing, I started probing around different test points. At some point I hooked 3.3V up to what was labeled as the +3V3 test point for some reason.

Then I heard a pop, saw magic smoke, and immediately assumed I had just made things worse.

Then I looked down and the green 3.3V LED was on. What???

Measured the rail again: 3.3V.

Turns out the silkscreen test point labels were wrong. That “3V3” test point was actually the EN pin between the MCU and motor driver. So by feeding 3.3V into it, I fried either the DRV or the MCU, and whatever burned open stopped dragging the rail down. In other words, I accidentally failed my way into a debugging success.

From there I started removing parts on a fresh board one at a time. I removed the DRV, still 0.84V. Then I removed MCU, and the LED came back. After another round of staring at the schematic, I finally found the real root cause: I had accidentally swapped VDD and VCC on the MCU. It was staring at my face the entire time. Talk about shame...

I ended up attempted three board surgeries and the third attempt finally worked with trace cuts and magnet wire, and somehow the CH32V006 survived reverse voltage on its power pins and still ran firmware afterwards. This little MCU is tough!

It's not a failure if I never give up, right?

I wrote up the full debugging story with photos and repair details here if anyone wants the whole mess.