[Making PCBs with magazine's paper]

My mate used the laser printer technique and it works a treat for simple/low-current circuits. i have one question with power circuits that need big tracks, is there any technique to achiev it without using an expensive solder flow machine (i notice on professional power pcb's they have a slight dome to the track) and if not is there any cheap uk pcb making places ?

[DTMF transceiver connection]

wow all this DTMF stuff sounds cool.

DAM IT dont side track me from another project !

+"I before E eccept after C" hehe ;)

[varible voltage, current limiting, power supply]

MylarHornet, i just picked up on you saying

[varible voltage, current limiting, power supply]

Hi, MylarHornet

ok its late so im going to go through what you said, in theory it sounds good and at a quick look its cheaper then this example (in the 'on' semicondutor datasheet)(thought it might be useful)

i just spent some time looking through retail psu's to get an idea of comman specs so i can design mine with the best usable features. i might include two adjustable postive rails and a single negative rail. Ive come to this conclusion after thinking about how iam going to be using it and certain situations back at uni where i had to use 2 psu's

ive hunted down the best price for spec transformer (well they all cost a fortune in the uk), 25v (DC 35.25V), 500VA/10A max(i figure if i have 2x1.5A max and 1x3A +other bits 10 should cover it), toroidal unit. Now im pretty much straight out of uni so theory wise it sounds ok and is also the cheapest transformer of its kind but is toroidal ok for this purpose ?

Anyway its by no means bought yet so if its wrong no problem ;)

[varible voltage, current limiting, power supply]

thanks ill have a look, ill draw up al my ideas into a design and keep all my developments to this thread ;)

i have had a look through the articles on this site and here aswell http://www.discovercircuits.com/P/pwr-variable.htm (moderators please delete if in-appropriate).

ive started to get an idea of the whole parts list and chassis dimensions.

If you want to use a micro-controller to display the voltage and current have a look at analogue devices ADUC812, an excellant microcontroller for applications like this, although it is abit excessive and

[varible voltage, current limiting, power supply]

Im currently designing (slowly as i have little free time) a varible voltage current limiting power supply, below are some of the features that i would like to incorporate;

(bare with me as i ramble and am in the design/thinking stage still)

varible rails
------------------
0 to +30v (Imax ~2A)
0 to -30v (Imax ~1.5A)

constant rail
-------------------
5v Imax ~2A

current limiting
-------------------
have no idea quite what todo but want to build this feature in

microcontroller
-------------------
AD 8051 (i got a couple of free samples, 14bit adc, 7 channels)
lcd measuring voltage and current.



Ok so i have read through google and this site and have got some really good ideas ;) The reason i have a constant 5v line is beuase i use 5v loads and want to be able to use other voltages at the same time.

Ive been looking at many ways to do things and pretty sure on most things except for the current aspect of the design. If i use the LM317 and LM337 (for the varible rate supply) (or the bigger brothers of these ic's capable of 3A and 5A) can i somehow incorporate current limiting?

+i trying to think of a way to measure current and am abit lost, ill probably use an op amp for voltage samples and then use the microcontrollers adc (5v input scale).

+if i want a constant rail as well as +/- 0 to 30v it means needing 2 transformers or using a 5v regulator although this isnt very efficient (burning off 25v) so should i simply use 2 transformers and 2 bridge rectifiers of pull everything off 1 transformer (they costs a fortune over here so id rather use 1)

thanks for any advice on what not to do or what i could do/use