help: Small PSU for microcontroller/retrocomputing - Page 1
Forum section: electronics / projects

author: irda86
author_rank: Contributor
timestamp: December 09, 2016, 01:36:31 pm
content: Hi,I'm looking for a small PSU for microcontrollers and small electronic projects.I think USB powered (from a 10W USB charger) should be ok.I would also like it to do 5V and 3,3V at the same time.Maybe have one of the outputs fixed and the other one variable?Has anybody seen something like that? If not, where should I look to do-it-myself?Alternatively, if it could also fit Commodore C64 and/or ZX Spectrum motherboards, it would be great.From this:https://www.c64-wiki.com/index.php/Power_Supplyhttps://www.c64-wiki.com/index.php/Power_Supply_Connectorhttps://groups.google.com/forum/#!topic/comp.sys.sinclair/yWNpi9FhR8wIt appears that it may be complex though.Are there DIY PSUs for retro-computers?

author: jeroen79
author_rank: Frequent Contributor
timestamp: December 09, 2016, 02:05:48 pm
content: Just get a pair of basic chassis mount AC/DC switchmode powersupplies and put them in a box.They come with fixed 3.3V and 5V outputs.Pick whatever current capacity you need.

author: madires
author_rank: Super Contributor
timestamp: December 09, 2016, 02:34:16 pm
content: If your intention is to experiment, repair and do small projects I'd recommend to get a small lab PSU which also provides current limiting. There are some cheap ones with 0-15V at 3A for about EUR 50. I haven't seen any dual channel PSUs in that catagory. You can also get kits, but with all the parts, case, meters and transformer they are more expensive than an off-the-shelf unit. Though, it's fun building them.

author: JanJansen
author_rank: Frequent Contributor
timestamp: December 09, 2016, 02:38:28 pm
content: Hi, the C64 already has 5 volt aboard, you can use that.Maybe add a 3,3 volt regulator for your MCU or use a 5v compatible MCU.

author: aries1470
author_rank: Regular Contributor
timestamp: December 09, 2016, 02:52:21 pm
content: what jeroen79 mentioned is the easiest and quickest solution and the voltages fairly well regulated.On the other hand, the links you have are for C64 power supplies. If that is the case, you need 9V AC, of which is a simple transformer, just getone for your location, of which France has 230V AC, so a 230/9v would be sufficient but please adhere to safety 1st.If you are going to do it all on your own, the easiest would be to put some rudimentary safety on the AC, and from the 9V output, you can use a 7805 and 78033 for the 3P3V or a variable version.You have not mentioned what your power draw needs are either, 100mA, 1000mA or more?Do youneed5V fixed all the time and the other one 3P3V or variable? How will you monitor the output voltage?What are your soldering skills, through hole only or SMT too?If you only need 500mA and SMT, here is a simple IC:LT3029

author: technix
author_rank: Super Contributor
timestamp: December 09, 2016, 03:01:22 pm
content: I often use an iPad charger for this, and if 3.3V rail is needed, slap in a TPS562200. The TPS562200 is a synchronized rectifying (no diode) switching regulator but it is fairly easy to use and requires no compensation.

author: irda86
author_rank: Contributor
timestamp: December 12, 2016, 02:47:56 pm
content: Quote from: jeroen79 on December 09, 2016, 02:05:48 pmThanks for your reply, do you have any recommendations/links for that?

author: irda86
author_rank: Contributor
timestamp: December 12, 2016, 02:50:53 pm
content: Quote from: madires on December 09, 2016, 02:34:16 pmThanks for your comment.Yes, the intention is to experiment.I'm looking for something small and modular (if I can use a standard USB charger or something of that size it would be good) and the lab PSU's I've seen seem quite big, would you have a good recommendation for the cheap ones you talk about?

author: irda86
author_rank: Contributor
timestamp: December 12, 2016, 02:53:12 pm
content: Quote from: JanJansen on December 09, 2016, 02:38:28 pmThanks for your comment, it's a good idea.However, right now I don't have a C64 PSU, I may get a C64 without PSU and that's why I'm interested in knowing if I can have a single PSU for multiple uses, C64, ZX, Arduino, etc.

author: irda86
author_rank: Contributor
timestamp: December 12, 2016, 03:02:32 pm
content: Quote from: aries1470 on December 09, 2016, 02:52:21 pmThanks for the comment.Do you know where could I learn some basic safety measures to put on the AC and/or the design of this simple PSU?I think using the 7805 is pretty simple, but I'm wondering what you mean with the safety measures.Quote from: aries1470 on December 09, 2016, 02:52:21 pmGood point.I'm thinking something like 15W should be enough, because IIUC the C64 PSU is around 10W and the ZX is a bit more, like 12W or so?Quote from: aries1470 on December 09, 2016, 02:52:21 pmWell, if I could get 5V + 3V3 + variable that'd be good, but I think most microcontroller experiments should be fine with 5V+3V3 right?What do you guys usually have? (I guess many people have real lab PSUs, but for hobbist I'm thinking it'd be a bit overkill)Quote from: aries1470 on December 09, 2016, 02:52:21 pmNever done SMT, but I've heard it's not that difficult.Quote from: aries1470 on December 09, 2016, 02:52:21 pmThanks!. Althought I'm thinking I would be needing more.If I use lots of LEDs, like those programmable LED strips, would I need a special PSU as well?

author: SL4P
author_rank: Super Contributor
timestamp: December 12, 2016, 08:22:31 pm
content: I've been doing this for years, and I always lean toward using fixed voltage supplies on the bench, and a variable only when needed.Why?Because it's so easy to leave or bump the variable up to a setting that will fry your device.I've spent probably $20 total over 30 years on decent quality closed frame supplies, and have an insulated spring terminal strip across my work area with 24/12/5 'always on', and a 0-30 @3A variable sitting nearby.If a project goes on the road, normally a salvaged plug-pack/adapter does the job.Your plan to use th C64/ZX supplies as hobby supplies is a little distracting.As someone pointed out, for example, the C64 brick is AC, so you stil need a rectiier and regulators - and probably heatsinks etc...If you're getting into electronics for the long term, build or buy a decent entry level DC power supply, you won't regret it. A dual rail variable supply is quite rea$onable. Ask here when you see one you like for safety advice and experiences.

author: irda86
author_rank: Contributor
timestamp: December 13, 2016, 02:32:33 pm
content: Quote from: SL4P on December 12, 2016, 08:22:31 pmWell, if I'm going to be doing this, better do it once.The idea is to to avoid having multiple PSUs since I won't be powering up all projects at once.Quote from: SL4P on December 12, 2016, 08:22:31 pmThanks. I would like to avoid heatsinks and go for switching regulators.Quote from: SL4P on December 12, 2016, 08:22:31 pmThanks. I tried going to adafruit and sparkfun, but found no DC power supply, any idea of where could I look for one?

author: irda86
author_rank: Contributor
timestamp: December 13, 2016, 03:16:03 pm
content: Quote from: irda86 on December 13, 2016, 02:32:33 pmOther than eBay/Amazon that is, I'm looking for a real seller with decent support and delivery times, not the kind that takes for ever to deliver and has no support.

author: ThomasDK
author_rank: Regular Contributor
timestamp: December 13, 2016, 05:42:14 pm
content: Something like this?Fixed 5V + 0-30Vhttp://www.tme.eu/fr/details/tp-1303/alimentations-multicanal/twintex/

author: brainwash
author_rank: Frequent Contributor
timestamp: December 14, 2016, 02:32:55 am
content: Another idea is to use those cheap (0.45$ on aliexpress) breadboard power supplies. They take up to 20V in, have a protection diode (so you can probably feed AC), provide selectable 5V and 3.3V to breadboard pins. They use linear regulators so I doubt you can safely draw more than 200mA for longer amounts of time. For the price I just ordered 4 of them, they are useful for parts as well.