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.

Yes a 24V transformer can be used but you will not get the full 30V plus you will suffer a higher ripple at max voltage set to max current, This would be ok if only want 25V PSU Yes you can use 2N3055 instead of TIP3055

This is my version of the PSU , All tested all working no problems complete with PCB and BOM aslo with connection drawing, I mounted the transistors on a seperate PCB but you don't have to use the PCB you can just hard wire them. EL_power_supply.pdf

I brought a kit from Velleman which was based om the ICL7107 and I found that this gave unstable readings and could never cure the bouncing of the readings, May be this is why they stopped selling it ? So in the end I decided to design and build my own based on the MAX7219 and PIC16F876, This gives accurate and stable readings and is now used in my Velleman PSU 0-30V 0-10A, I used ISIS to simulate it to get everything working(Picture attached) and then designed and built the PCB for it. I like the idea of LED'S because where my PSU sits at the back of the bench I don't have to lean forward to see the LCD version. Plus I use the green version which is better

I forgot to add the latest schematic to the PDF file Picmaster Schematic_Prints.pdf

Here is my vesrion of the power supply comlete. PDF file is a new BOM(for this project only),PCB copper side, PCB overlay, assembly drawings Please let me know if you find any errors or suggestions Picmaster

Here is the working version on my PSU, There is just just a couple of minor things I have got to look into and clarify. Yes the connecting wires may look a little on the light side but this is for testing only Has I only took to 3amps and calibrated max current for a few seconds to try. These are the minor things that I have got to look into. 1. Because I'm using a 30V transformer the voltage is slightly to high feeding the op-amps has the TLE2141 is only rated at 44V I got 48V. 2. With the current pot set to Min the limit LED comes and and this restricts the voltage I have to turn it up slightly(not sure what the voltage is at the center of the pot has it is getting late.) Aslo I'm not sure if this is normal if the limit LED should light up with the pot to min, I did disconnect C10 has if I remember lighty had the same trouble but it is still the same I get full control over the current range min current is about 40ma, I did see that is should only be 12ma, I will have to make sure that I've got all the correct components in place first and I will read through the older posts.

I've got it 3/4 built, I missed some parts off and by the time I thought about it Maplins was closed. will try and get them tomorrow (Monday) then I will be ready for testing and if all goes well I will upload the pcb picmaster

This is the connections drawing for my version of the power supply and updated schematic, To me it looks quite simple This is the actual size of the PCB and what the layout looks like. The next thing is to update the component values on the schematic and create BOM Hopefully over the weekend I shall get PCB made and assembled POWER_SUPPLY_V2.pdf power_supply.pdf

This is only the schematic I have a drawing explaining all the connections in detail, I t will be simple to follow, I'll upload the details in a short while Picmaster

Thanks for that, I did for get to add the resistor to the BD139, The reason is I had the idea of having the BD139 and the ouput transistors and the emitteres resistors on a seperate board so they can bolt direct to the main heathisnk rather than have 2 heatsinks for them. I wll sort that out either add them to the main board or go back to the first idea,