Measuring negative voltages with a PIC

Hi Eric,

Thats cured it mate. All working fine now.

I tweaked the voltage pots last night too and got them reading within tolerance, well less than 1% I reckon.

Just had another thought though. It might be handy to have one line reading +v and -v and the other showing probe volts.

That way I could see all in one what volts I am putting in and what is showing wherever I put the probe. One question though. What happens if I try to measure a negative voltage with the probe? Will it hurt anything?

Al

bigal_scorpio said:

Hi Eric,

Thats cured it mate. All working fine now.

I tweaked the voltage pots last night too and got them reading within tolerance, well less than 1% I reckon.

Just had another thought though. It might be handy to have one line reading +v and -v and the other showing probe volts.

That way I could see all in one what volts I am putting in and what is showing wherever I put the probe. One question though. What happens if I try to measure a negative voltage with the probe? Will it hurt anything?

Al

Click to expand...

hi Al,

A negative should not cause a problem with LM358

Look a the 750mS conversion time for the DS18B20P , also the hard pull up time, I think the P is not suitable for the Basic routines I have .

Eric
BTW: I am getting a few components together for you, will post in the next few days.

Hi Eric,

The 18 should be at your place tomorrow, barring postal breakdowns anyway.

I have been studying the LM part and it does seem pretty accurate and easy to use to boot. Though on my current project it would mean finding another ADC input which I have just used for the probe, which is a really good idea! the more I think about it the more useful it seems.

But next time I need a temperature measurement I will probably go for the LM, unless I use a PIC with no ADC of course

Anyway as I said before the PSU is really superb now and has everything that I wanted and more! I would never have got this far without your help mate.

Al

hi Al,
Will you post photo's of the working unit.?

Eric.
OT: let you know when the post arrives.

Hi Eric,

Sorry about the late reply but we are still in shock here. Car went for MOT and needed some bushes, ended up with shrubs and trees by the price of it!

Here are some pics of my PSU under different conditions, pos and neg volts, sum volts & ampage and case temperature, fan condition etc. I'm not being patronising Eric, the above descriptions are for people who are maybe looking at the page for the first time and unlike you have not virtually built the thing.

The shot of the back shows from left to right the rail switches, one each for pos and neg volts, also the temperature set switch and the 5v rail switch, and of course the mains connector.

The front controls are as follows:-
Top row - 5v, 0v, LCD display, Pos variable voltage, 0v, Negative variable voltage.
Bottom row - On/off, Probe port, 5v current limiter, display option knob, pos rail current limiter, pos volts regulation and neg volts regulation .

Next time I open the case I will get some pictures of the innards though they are nowhere as neat as the outside!

The only thing left to do is the decals for the switches and controls but I'm still working on them in photoshop.

Al

BTW does anyone know the name of the connectors? They have a banana socket and a sprung wire clip, but besides the ones I had I cannot find them anywhere for sale, probably as I don't know what to search for.

Hi Eric,

Did you come up with any ideas for improvements or additions yet?

Al

bigal_scorpio said:

Hi Eric,

Did you come up with any ideas for improvements or additions yet?

Al

Click to expand...

hi Al,
You have RC4,5 and B1 unused on the PIC.

Perhaps a 1KHz square wave output on RC4 when Pos4 is selected

You could change PB0 [ DS18B22] control to say PortB.1 and uses PORTB.0 as an interrupt on change event detector.

What sort of projects are you working on that could be helped with additional features.??

Hi Eric,

Hmm, square wave. Sounds interesting. As to the projects, I don't particularly have anything in mind that needs other features. I am just trying to future proof the PSU, so in a years time when I am building the walrus polisher or whatever then I will have the tech ready to do it. Plus I actually enjoy doing it. The things I have been occupied with in the past seem to have dried up at the moment and I need to be doing something all the time.

It doesn't matter what I'm doing so long as it keeps me occupied. I hate not doing something and with the old body starting to fail I have had to give up the spot on the British gymnastics squad and such.

I just like to tinker and keep whats left of my mind working, so any suggestions for the PSU or any other project would be great.

Al

CMOS rail-rail opamps you can use **broken link removed**