Since SID (http://http://dangerousprototypes.com/forum/viewtopic.php?f=56&t=2457) project is basically done (it works as well as I need it to and has enough there for anyone who want new features to be able to do so) I'm starting a new project (as I mentioned) that's something like programmable load but little bit more.
Here's *what* I want to be able to achieve
1. connect the voltage source to the "device" (0-32VDC)
2. connect the output from the "device" to the PSU under test
3. connect the output from the PSU under test back to the device
Set start load value (in mA), set end load value (in mA) set step and time each step is to be measured (averaged) and run the "device". Measure the input voltage,current, to the PSU under test and the output voltage, current (set by mcu) of the PSU under test, graph the raw data + calculate efficiency (output V*A / input V*A) and graph it too.
IO that I want to be using
- rotary encoder with button + 1 or 2 extra buttons (not sure if required or not)
- 320x240 BW display (available cheap at sure, itead and iirc seeed also)
- optically isolated communication with PC (since this is a very slow and simple communication and optically isolated usb cost arm and a leg, I'd go with simple uart isolation + some 1$ usb2uart adapter ... uart isolation can be done with special chip or maybe just an IR led like what you can see on multimeters ... not to mention firmware gets 100x simpler with only uart)
Another important issue is I'd power the whole "device" from isolated power supply. I seen some 5V:5V isolated regulators for few dollars so they should get the job done (for e.g. SIM1-0505 or SIM1-1205 or SIM1-2405 .. you can find them at reichelt (http://http://www.reichelt.de/Wandler-Module-DC-DC/SIM1-0505S-DIL8/index.html?;ACTION=3;LA=444;GROUP=P853;GROUPID=4956;ARTICLE=35039;START=0;SORT=artnr;OFFSET=16;SID=12TgJC938AAAIAAGnRMHI04b8efd55d6d4546a6d16009f9b884ed) )
The schematic should be simple.
Since I want to have the whole thing "isolated" I'd use high side current amplifier op-amps (differential amp's) on the shunts to measure the current. I need 2 of those (for input and for the load), I might add some selectable gain or programmable gain op-amp after them in order to get the higher resolution in the 1mA region (100uA I think is easily obtainable). I need a DAC to drive an op that's driving some beefy FET on some AMD CPU heat sink (have few of these :D ) and that's basically all .. should be fairly simple
ah I almost forgot, this is attm in "idea" stage, if you know of similar project (the closest one I know is overload and it's not "good enough" imo) please lemme know as I'd rather improve on existing design (or use existing desing if it works) then waste time and design from scratch :D
i have been playing with the ts1100, there are many gain options from 20 to 200. and rated up to 1 amp. the best part is thier in an easy to solder sot23-5 pack.
@0.65usd there are not bad, but will not output untill input voltage is above 0.8V from ground. needing only a simple resistor and a single cap to operate this is very space saving.
well I'm discussing it today with arakis and he mentioned some very nice parts like MAX9611 MAX9612 MAX4210 MAX4211 LTC4151 ... that I kinda missed ... so basically there's a i2c/spi current amplifier with built in comparator so you just add DAC on the set pin of the comparator and you drive fet from the comparator output and there's your digital programable load ..
I found perfect LCD for this project: ITDB02-2.2SP (http://http://iteadstudio.com/store/index.php?main_page=product_info&cPath=57_58&products_id=527) (18$ at itead, 2.2" 176x220, 262K color with SPI input, so not super fast but super simple to drive with great display capabilities)