PicMaster

Hi All I'm working in a project well a simple pic multi-meter based on on bench power supply one I have working ok, Now I want to make a portable meter of it now this would be ok if you made sure you got the connections the correct way roun, I know I could add reverse polarity diodes but I would like to some how have it where it does not matter how you connect the leads to the input the output to the ADin pin on the pic would read say 0-2.5V if the leads wrong way round(where I could display a - sign) and 2.5-5V if they was correct way connected or same again no matter how the leads are connected I get 0-5V to the ADin pin and then can add a circuit to go high and the pic chip looks for this, Now I've tried a differnational configured op-amp but no matter if there is no leads or whcih way round they go I always get a 5v output, Now this may be the way I had it set up. What would be the best method and the correct way so no matter how you connect the leads up you get a 05V out to the ADin pin hope you can understadn what I'm trying to explain what I'm doing Thanks

I was able to open it try this one I've zipped it up see how you get on Placa_principal.zip

why do people need to waste time on simulating the design beats me, The PSU works perfectly has it so in my eye why try and reinvent the wheel. I've found from past experience simulating don't always to seem to work like they do in real life. you can't feel the monitor for heat ;D

Thanks for the comment,

You could not have set voltage anyway, You could set the voltage with the wiper but you would have no way of limiting it, if you where to move the pot. The only way would be remove pots and use PWM from the pic. The same goes for the current control. You can read real time voltage,current and temp of the heatsink, I did sometime time ago remove the pots and used pic to control the PSU but never got around to finishing it may be I will blow the cob webs off it and start again.

I remember now why I created a new BOM is that some of the parts do not exist now like the .33R power transistors resistors . I will check that all the values are correct and I have decided to leave my version has it is, After all it is so simple to cross reference between the two drawings and BOM but I can't see the reason or nay need to, Has I built my PSU off my version including the bom. I will correct the last sheet which is the Assembly drawing morpheous87 I would try 47R then 51R and just increase it a little until it works, I never had this trouble with mine

R17 is R16 on my schematic They are both laid out the same order so you can cross referaence from the original version. If I get time I will correct my version so it's the same has the original

I will look into it and let you know, Your the first one to spot it.

So you have used Audio's schematic ?, Did you redraw the schematic and then transfered the design over to the PCB package then once you laid it out you ran the DRC rule checker ? or Who's PCB layout you used ?, The only reason I ask is if you have just laid out the PCB yourself just from the schematic then you could have errors in your PCB. When I did mine I redrew the schematic check it and double check it against the orginal then transfered the design internally to the PCB package, Then Laid out then design then ran the DRC rule checker this tells me that it is 100% routed and error free. Mine worked first time has it should whenI built mine.

Looking at your PCB the output tracks are still not big enough to take the current for 5A and yes the pads need upgrading. Here is the modified version this will either do the 3A or 5A version, For the 3A just leave out Q3A & R20A For the 5A change R7 must be 0.27 ohms/10W (TB4 or the 2 holes either side), I have not updated the BOM yet but should be easy to workoutEL3-_5A_PSU.pdf

Yes it will require a little Mod, I only built the 3A version I've never really as the need for 5A, The mod is esy to do you can just hardwire the third transistor onto the exsisting tracs just solder the emitter resistor straight onto the pin of the transistor. I can mod the pcb to take the thr third transisor

Yeah I did and you can download it from here, It's single sided and it can be 3A or 5A your choice

I never had that problem, Have you checked that the bridge rectifier is correct ? I used one like this from here http://www.rapidonline.com/Electronic-Components/Discrete-Semiconductors/Bridge-Rectifier-Diodes/4A-8A-In-line-bridge-rectifiers/29673 It's like audioguru stated it must have been power supply voltage is connected backwards or the op-amps aren't the correct ones. Has it is remover U1&U2 and see what voltage you have got on pins 7&4. Or have you found your error or a fault, means you thaked audioguru but you do not say if problem solved I know my design works 100% otherwise I would of not published it

You could do what I did went to the Texas instruments web site and ordered some samples then you get them for free. You need to listen to audioguru the old design has many faults, I have ben there and done that tried everything to get the old design to work but in the end it went in the bin and I designed my own PCB of the upadted schematics and have had no problems. There is lots of information in this topic.

It is sized 1:1 and it does not need to be mirrored. When you go to print it just make sure the the page scaling is set to none, This is how I did mine and it worked perfectly.