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Topic: Computer controlled PS/function gen/multimeter (Read 229245 times) previous topic - next topic

Re: Computer controlled PS/function gen/multimeter

Reply #210
[quote author="fenugrec"]As I see it, using an FTDI vs PIC wouldn't make an isolated PSU more simple or complex, just different. Here are some possibilities :
Code: [Select]
; FTDI, single isolated output
USB <=> FTDI <=OPTO=> PIC => regulator

;FTDI, dual independant outputs
USB <=> FTDI <=OPTO=>  PIC1 (regulator)
             <=OPTO=>  PIC2 (regulator)

;same, PIC-based
USB <=> PIC <=OPTO=>  PIC1 (regulator)
            <=OPTO=>  PIC2 (regulator)

I would personally go for the last of these; having a PIC to arbitrate the opto-isolated bus is better IMO. We can also program it to send a "keepalive" signal to the slave PICs : in case of a USB comm failure, disable the outputs or take other safe actions...[/quote]

Agreed, but, to your list, I would add :
Code: [Select]
; PIC-based
USB <=> isolation <=> PIC regulator(s)

I do not recall the pricing, but there are USB PHY isolator chips which would sit between the physical USB device jack and the PIC, thus isolating everything on the board.  As we discussed, all power for the µC could come from the power supply input, allowing the USB to be used purely as a differential data transport and nothing else.

Re: Computer controlled PS/function gen/multimeter

Reply #211
The LM317 is just a 1.25v version of the lm309/7805 style regulator.  It can be used fine without the resistors, you just supply 1.25v less than the desired output to the ADJ pin.  This needs to be able to sink up to 0.1mA.  Also, the minimum load is 10mA.  The resistors normally act as this minimum load and use cheap components to set the output voltage based on the internal regulator.

Also, some of the messages in this thread seem to forget that most voltage regulators have a minimum drop, in the case of the LM317 it's 3v.  So for 12v out, you need at least 15v in.

Re: Computer controlled PS/function gen/multimeter

Reply #212
Found this via HackaDay. Might be a good example for regulator stage design.

Re: Computer controlled PS/function gen/multimeter

Reply #213
Hi everybody!

In the newsletter from Maxim, I saw a good application note and wanted to share with you. It is for SMPS design mostly but some parts may relate to linear regulator design also.

Re: Computer controlled PS/function gen/multimeter

Reply #214
Is this project alive?  It sounds pretty awesome.  I haven't read anything new about it. I would be sad if it died.

Re: Computer controlled PS/function gen/multimeter

Reply #215
[quote author="Colfaxmingo"]
Is this project alive?  It sounds pretty awesome.  I haven't read anything new about it. I would be sad if it died.
[/quote]

It's still just at the "idea" stage. Personnally I don't badly need one of these, and I'm a bit short on time.
However, there needs to be practical experimentation. There were many cases of "this should be built to verify it works" that still remain to be tested... and last time I checked there was still a lack of concrete engineering, i.e. knowledgable design. I drew up a lot of schematics (not all good), and rsdio + another member seemed to know what they were talking about but none of us logged much serious design.

If you're handy, I would say there's enough material in the old posts to let you build something that will most probably work. Not necesarily safe / reliable / stable / performant though.

Re: Computer controlled PS/function gen/multimeter

Reply #216
it may be unnecessary to have it computer controlled a simple lcd and a micro should work, 2 or 3 channels output would be more than necessary.

Re: Computer controlled PS/function gen/multimeter

Reply #217
[quote author="sqkybeaver"]
it may be unnecessary to have it computer controlled a simple lcd and a micro should work, 2 or 3 channels output would be more than necessary.
[/quote]

The plan was that the computer would give some set voltages to a micro (18F series maybe), which in turn would use the components on board to give the requested voltage with current limitations. I already had a control module hack in mind (I ordered a bunch of rotary encoders and a keypad plus I have easy access to LCD screens). The project is kind of "in sleep" these days, my guess: because we couldn't converge on a design everyone got bored.

But after my finals I'm planning to "wake up" this project, even if it's only me working on it.

Re: Computer controlled PS/function gen/multimeter

Reply #218
Keep it coming! I'm going to at least buy one if it doesn't take years to come ;) If I can help (time, skills...?) I'd be happy.

Re: Re: Computer controlled PS/function gen/multimeter

Reply #219
I saw this site and it made me think about this thread... so i'm pulling it out and adding this link that may give more ideas.  I'm not smart enough to judge if it's any better or worse than the suggestions already presented.

http://www.electrobob.com/digital-power ... -1-concept

Re: Re: Computer controlled PS/function gen/multimeter

Reply #220
I have the tuxgraphics one and it works well (was mentioned earlier in the thread).

I'd like to build something similar, but as a switching power supply. Essentially a microcontroller driven buck converter. Its main advantage would be that it can deliver more current at lower voltages without wasting most energy in a huge heatsink.
Markus

Re: Re: Computer controlled PS/function gen/multimeter

Reply #221
This was discussed and we decided to use a linear PS circuit because of less noise. But I still feel like using a switching supply.

I got my hands on a power supply test kit from TI by Element 14 a little while ago. We can use some design parts and algorithms in this project IMO. I just have to go back to Japan and finish moving into my new house. :S

Re: Re: Computer controlled PS/function gen/multimeter

Reply #222
I'm working on a small/simple version of something like this, now that seeed has dropped prices. My plan is to use a smps brick (or more likely old laptop adapter) and some linear regulators to provide 3.3v, 5v, and an adjustable from 0v->whatever. I do not see an easy way to add adjustable current limiting to standard regulators. My plan is to make it interface to a simple 16x2 or even 8x2 LCD and provide current measurements on the 3.3v, 5v, and adjustable line, as well as voltage on the adjustable output. The uC will control the voltage out instead of using a multiturn pot it will probably just use a rotary encoder.

I'm hoping to use all SMD but hopefully no very fine pitch parts. It will definitely fit in a 10cm by 10cm seeed board and possibly a 5cm by 5cm (maybe). Once school is out I'm going to start working on some PCB mockups/layouts.

Is there a simple/straightforward way to add adjustable current limit to a LM317/LM350 style reg? Or do you pretty much have to build the regulator from discreet parts?

Note: I haven't decided if it's really worth adding a USB interface or not. Since it will probably require isolation and the like. It might be worth just providing uart in/out, so it could be connected to an external isolation & interface circuit.

Re: Computer controlled PS/function gen/multimeter

Reply #223
what about using a spi 16bit DAC to control the reference  voltage for the error comparator in lm78s40. it would lower the noise from the PWM/filter design.

similar design could be used with a lm723 liner precision regulator, and the current limit could be controled via a RSense in parralel with a 1k digital pot. from witch the wipper could be conected to the Rsence lead of the 723 IC
best regards FIlip.

 

Re: Computer controlled PS/function gen/multimeter

Reply #224
[quote author="arakis"]what about using a spi 16bit DAC to control the reference  voltage for the error comparator in lm78s40. it would lower the noise from the PWM/filter design.[/quote]
Good point.  PWM is probably a cheaper solution, but noise issues could easily make it worth the extra expense of a real DAC.