Lab Powersupply - Markus take

[markus_b]

Just a short update: I got the PCB's the day we left, so I took a set of tools with me and started working on it as time permits. I've now assembled the 3.3V supply, the microcontroller and the LCD display. The microcontroller and display are essential for future progress so they came first.

I've found two errors and a problem up until now:
- The 'out' pin of the 3.3V regulator was not connected, the error is in the schematics, too
- The 'gnd' pin of the LCD was not connected. This probably comes from the flood used for ground, so there are no hairwires for Gnd
- The problem is that the connector for the display is backwards, it must be turned by 180°.

Right now I'm working on getting a library working with the display to be able to write on it. It initializes fine, but there is no character generator, so I need a library for that.

[Strada916]

Hey Markus just wondering if you have any updates?

[markus_b]

I'gotten distracted by other stuff during summer, family vacation was one, the pending sailboat recovery was the second. At the moment work is quite intense, so time is limited.

However here the state:
- The micro and LCD is working fine, ADC, DAC, displays, UART, rotary knobs are up and running.
- Voltage control works (the output voltage follows the DAC)
- Current control does not work, needs investigation. I think there is a problem with the circuit, maybe the OP-amp does not like to work closely to the rail.
- The switching part is not yet tested at all (got the wrong inductor)

I fear it will be end of the year, before I have significant progress.

[Strada916]

Markus. You sound like a busy man. Hope the sailboat recovery is successful. Look forward to further updates as your time permits. I only asked because we have not heard from you in ages. Is all. See you at the next update.

[brainwash]

Have you thought of putting together a kit? I would probably buy one if it was available for a decent price.
Don't know how mouser works but tme.eu usually has better prices on components, I've dealt with them in the past. Unfortunately you need a VAT number to see the prices and deal with them but it's not a huge problem.

[crispus]

Don't know how mouser works but tme.eu usually has better prices on components, I've dealt with them in the past. Unfortunately you need a VAT number to see the prices and deal with them but it's not a huge problem.

I frequently order from tme.eu, but I don't have and I don't need a VAT number. From 2011 I think this is not needed anymore... And the shipping is about 4 euros

[peter.mitchell]

This is one of those things where I'd love to throw money at it to get it done faster but know it wouldn't do much at all. I can't wait to see this finished, i would definitely get a few made, it's very hard to find something nice that isn't stupidly expensive or shoddily built.

[cynikal]

bump, any news on this? Seemed very promising and right up my alley as far as DIY PS needs go (and i'm learning a lot along the way which is the real draw for me here).

I actually wanted to work on a similar design as well, but some of this ee/ps design stuff is just slightly over my head (i'm still treading at least though), but i really am a fan of the BYOPS approach (bring your own power supply, for the unregulated input that is) and am thinking of using some Cisco 6500 Switch power supplies, i have a pair of 1300w ones (and they're about 30-50 bucks each) and also combining those (plus the variable PS markus was working on) with a more traditional (read: simpler for me to make) dual pos/neg rail fixed series of voltages (for some audio amp projects).  The PSs i have, put out 42v @ ~27amps, 12v @ 12amp, 5v @ 10amp and 3.3v @ 15amp (which sounds like a lot of current for 3.3v but i guess the cisco switches had a lot of 3.3v chips/devices Have the pinout from an internal cisco document to guide me wiring up and knowing how to interface with it

Anyway I can handle the converting the 42v down myself to a LT3083 friendlier level (which per the spec sheet is 23v? Why is OP pre-regulating up to 2-32v) but wouldn't mind seeing the AVR code to drive the LCD/interface with the rotary encoders/generate the control voltages.  Have an IT/programming background (done a buncha scripting/coding in sh/perl/python) but my C is a bit rusty so that part i wouldn't mind some help with.  Also would be interested in buying a board if it could be adapted to my needs somehow (or i guess i can customize my own design as needed).  Hope this project keeps making progress tho!

[brainwash]

http://gerrysweeney.com/category/projects/

Have a go.
If you are inexperienced you should settle for a low-amp supply. I used a 2A 2-15V supply for years and rarely needed something beefier. Make sure it has over current protection (adjustable current), you'll trip it a lot.