Multimeter testing at higher voltages

I needed a way to test out my HP 3478A multimeter at higher voltages. I ended up driving a transformer with a signal generator, then running the output directly into a voltage doubler. IMG_0772

Unfortunately the reverse breakdown of 1N4148 diodes is only a little bit above 100V. The solution (as seen above) is to simply run a few in series. I used a ceramic capacitor on the input, and an 0.47uF X2 rated filter capacitor on the output. Not really designed for high voltage DC, but it did the job! I was able to squeeze 426Vdc out with effectively no load (10M ohms).

IMG_0774

Lowering the amplitude from the signal generator gave me the 300V max the 3478A will take:

IMG_0773

 

Conclusion: It isn’t too hard to generate high voltages with readily available parts, and my 3478A works as expected. I didn’t even electrocute myself! Seriously though.. a little caution goes a long way.

Just a little dust..

IMG_0754

 

I found the inside of an Agilent 33120A looking like this. It runs a little warm without being covered in a blanket of dust! No wonder the output amplifier failed.

Power Supply Death

Power Supply Top

 

A few months ago I was rudely awoken in the middle of the night by the “exciting” smell of burning electronics! I got up fairly quickly and wondered what I could have possibly left on. It turns out it was not a project of mine, but (after some smelling around and unplugging of everything within sight,) my PC power supply. 2AM is a great time to catch fire!

As the pictures show there was a small scorch mark on both sides of the PCB. A blackened resistor is the culprit. I believe the root of the problem was bad capacitors possibly shorting out a power rail. The PSU was making some high frequency noise previously, notoriously caused by bad caps.

To get this far into the power supply I had to pull a lot out. It ended up being a good source of some components, but I never planned on repairing the supply. A good capacitor has already come in handy temporarily repairing an old HP 3478A.

Overall the events could have been worse than what happened, however, I would have hoped a fuse would have blown well before the power supply failed like it did.
Power Supply Bottom

ViaCar Sensors

ViaCar SensorsA quick picture: a group of sensors for ViaCar(NatCar) I made during my last year at UCSD. More to come when I get the chance to photograph everything, check out the projects page in coming weeks!

 

VHDL VU Meter

VU FPGA

There is a video at the end of the post, check it out!

This is a pseudo-VU meter written in VHDL. I did it for an afternoon project to see what I could do with VHDL quickly. I take the line level audio output from my computer and run it through a Schottky diode ( half wave rectification ), and then straight into a serial ADC. The rest is done on the Xilinx Spartan 3E FPGA.

A true VU meter would translate the volume level of the output signal to a certain DB level. Mine just peak detects the output of the ADC and then scales the output until I get good dynamic range out of the LEDs available. The end result could use some refinement, but I was happy with the rough draft.

I need to clean up my VHDL. I will have it up on github sooner rather than later!

VU ADC