I’m OUT OF STOCK of my FiveFish Electronic Load PCB and I think it’s time to re-order a new batch of PCBs. But rather than just re-ordering the same boards, I decided to improve it a bit.
A couple of weeks ago, I tried incorporating a 5-digit LED Voltmeter (bought from eBay) directly on the PCB. My attempts were crude, but the results were great.
The Electronic Load has a “current sense resistor” (equivalent to 1-ohm) and by measuring the voltage drop across this current sense resistor and using Ohm’s Law, we can compute the current flowing through our Electronic Load. I = E/R ; where I is the current flowing through the load, E = voltage drop across resistor and R = resistor value in ohms. I mentioned my current sense is “equivalent to 1-ohm.” That deserves a little bit of explanation. Rather than buying (1) high wattage, precision resistor, I decided to use several low-wattage, 1% resistors which are cheaper. I’m also using “load sharing” by using (2) Power MOSFETs in parallel instead of just one. So each MOSFET has 10pcs of 20-ohm resistors in parallel, and since I have (2) MOSFETs, each MOSFET only sees half the load. This comes to the equivalent of (20) paralleled resistors, each having a value of 20-ohms, for an equivalent resistance of 1-ohm. 
So now, all you have to do is connect a multimeter across this “current sense resistor” and take a voltage reading. A reading of 1 milliVolt will be the equivalent of 1 milliAmp flowing through the resistor (which is also the same current flowing through the MOSFET, which is same current flowing through the Electronic Load).
But connecting a multimeter is cumbersome, beside the fact that we’re using a valuable tool just for this one simple task. (It’s great if you have multiple meters in your lab, but sometimes you only have one or two.) It also makes for a very messy setup.
So I found this 5-Digit Voltmeter on eBay for approximately $6.00 + shipping and it’s surprisingly very accurate! Surely, this little voltmeter can take over this task, thus allowing us to use our our more expensive multimeter for other important duties. The 5-digit voltmeter has (4) wires. Two (2) of the wires are for supplying power to the voltmeter. The supply voltage can range anywhere from 3.5Volts to 30Volts. The other (2) wires are for the input measurement, called VIN+ and VIN-. These 2 wires connect to the voltage you want to measure. The measurement range is anywhere from 0.0000 Volts to 33.000 Volts. Accuracy is 0.3%, and displays (5)-digits for voltage readings below 4.3Volts approximately. I added solder pads on the Electronic Load PCB for these (4) wires required by the voltmeter. I also moved things around to make room for the Voltmeter Module. 
Right now, I’m not sure what to do about mounting. On my prototype, I just used double-sided tape to secure it to the PCB. But I know this solution isn’t long term. One can also use hot-glue to attach the voltmeter to the PCB, or JB-Weld. (But JB-Weld seems such a permanent solution, and don’t want that.)
A possible solution is using L-brackets. Then using a small piece of PCB, acrylic, or aluminum panel with a rectangular cutout for the Voltmeter, one can mount the Voltmeter vertically. You just need to secure the panel/plate to the L-bracket using nuts and bolts. 
And here’s the modified PCB, with the appropriate mounting hole for the L-brackets.
And here’s the final PCB design incorporating all the changes above. 
I’ll place the order for this new PCB version and within a week or two, you can purchase these PCBs at http://fivefishaudio.com/diy/eload/
And here’s a customer review of our Electronic Load:
Hi, Just finished assembling the FFA e-Load and it is everything I had hoped for! It is very stable and easy to use. The current sense tracks very well which was a pleasant surprise. I would have found lesser performance to be quite acceptable especially for such an inexpensive device, but this gem functions much better than merely acceptable! A very good design overall. I couldn’t be more pleased! Please feel free to quote me in your reviews if you wish. Thank you so much, Jerry Thiel
