Looking for adjustable voltage source project - Page 1
Forum section: electronics / projects

author: Martinn
author_rank: Frequent Contributor
timestamp: August 10, 2022, 05:47:49 pm
content: Hi all,for experimenting with discrete amplifier circuits I'd like to have a source for maybe two (4?) variable voltages, say +-10V. Simple solution would be 10-turn potentiometers. But of course much nicer would be a device with display, encoder...Calibrators do that, but are much too expensive for this purpose. A simple device with microcontroller and 2-4 channel DAC would be sufficient. Is anyone aware of a project like this?If I would do it, I'd simply use off-the-shelf components (reference, DAC, OPs) from the (not too) top end (let's say <$50 total) and see how far this would get me (without any LTZ1000 style fiddling). Maybe 20 bit DAC (4xDAC1220? OK make it $100), best $10 reference and so on. But still this is a lot of work, from power supply (make low noise +-15 V from what battery), microcontroller, display, USB, calibration EEPROM, analog part... all limited if possible to JLCPCB assembly parts (did enough manual SMT assembly for a lifetime). This would be a great apprentice project...So if anyone is aware of an existing solution/project that can be bought/built with reasonable effort/cost, I'm interested. A quick search on Aliexpress turned up nothing, maybe not something the maker crowd would need.EDIT: It seems there is a handful of DAC1220 boards on Ali. No display though.EDIT2: Couldn't resist doing a quick search what I would use:Power supply: 9V alkaline battery, 3.3 V and 5 V LDO, extra filtering for 5V analog (maybe 5.1 V for DAC1220)Traco TEC2-1223WI DC/DC module from 9V to +-15, heavy filtering (L-C-L-C-L-C with large ferrite beads) for reasonably clean +-15V (maybe extra high PSRR LDO to +-13-14 V)Analog: MAX6126 2.5 V reference, 4xDAC1220, OPA182 for 0-5 to +-10V conversion and output bufferingDigital (mostly this would be copy+paste from a recent project): STM32G0, 24C02 EEPROM, EA DOGXL160 display (without backlight - needs to much power), Encoder, KeypadMaybe throw in USB interface... (I think this is called feature creep)Thanks, Martin

author: ledtester
author_rank: Super Contributor
timestamp: August 10, 2022, 07:03:06 pm
content: Instead of the DC/DC converter I would just use four 9V batteries to get +/- 18 V. Doesn't sound like you need much current anyway and it'll be a lot cleaner.

author: Someone
author_rank: Super Contributor
timestamp: August 10, 2022, 10:15:52 pm
content: sounds like re-inventing the variable power supply modules that are already available dirt cheap:https://www.eevblog.com/forum/blog/eevblog-1030-$20-diy-bench-power-supply!/

author: Martinn
author_rank: Frequent Contributor
timestamp: August 17, 2022, 06:44:59 pm
content: Quote from: ledtester on August 10, 2022, 07:03:06 pmVery good idea. However, there are a number of drawbacks: Over the lifetime of the cells, voltage varies a lot (10.8 to 19.2 V seems realistic) - regulate to which fixed voltage? Battery supervision needs three ADC inputs (+9, +18, -18), I'd need a three pole switch (unobtainium) etc...So in the end I decided to go with the DC/DC converter. I'll see what my filtering skills are worth. Interesting reading:https://www.analog.com/media/en/technical-documentation/application-notes/an-1368.pdfQuote from: Someone on August 10, 2022, 10:15:52 pmThat was my thought also. Unfortunately only 10 mV resolution and probably super noisy.BTW I dumped the DAC1220 because of the exotic support parts and the limited INL spec. Went for an integrated 4x16 bit DAC instead.- Martin

author: alm
author_rank: Super Contributor
timestamp: August 17, 2022, 07:36:55 pm
content: For a ready-made product, the PDVS2mini comes close, though unipolar and more expensive:https://www.ianjohnston.com/index.php/onlineshop/handheld-precision-digital-voltage-source-2-mini-detail

author: MasterT
author_rank: Frequent Contributor
timestamp: August 17, 2022, 08:16:04 pm
content: MCP4725, or digital pot MCP4151 will be o'k.