After seeing your video i was inspired to take your design a step further and produce an 8-bit adder using the same logic of a ripple carry adder.

I've expanded your schematics to incorporate the 8-bits and everything the same. Unfortunately i don't know anyone who is good at circuit design so i can't really ask anyone if I've got the right stuff down on paper. Would you mind taking a quick look at my logic and schematics so i can be sure I've got everything right before i go off ordering a board that doesn't work.

I fixed the typo with the +5v which should have been +9v. Anything else i may have missed?.

Thanks for your time , your project was truly inspirational!





And this is the control board that I'll use. I know im missing X4-1 which should be a +9V output(down the bottom). Also did i wire the LED correctly?, i wanted it to switch on when I've got the switch closed but turn off when its open to show that the board is on and off(the one down the bottom of the page with the battery cell).

Hi

I'm glad you liked the project I gave your diagrams a quick once over and I didn't see any issues with the logic or schematics. I would suggest that you compare yours and the original by hand though checking the two schematics wire-by-wire to be 100% sure.

The only issue you may see is that this design (simply to save cost) uses NPN small signal transistors instead of more efficient components such as FETs. The effect of this is that, for each switching stage, you loose power across the circuit. This is why the output stage has transistor switches. I don't think it should be too much of an issue, but without testing and measuring it's hard to be sure.

Good luck!

Thanks for the quick reply!, I've sent my designed circuit board off to BatchPCB. I'll let you know the results when I get them back. Once again thanks for the help!

Also i did consider using FETs but I wanted to keep things simple and cheaper so I assumed the loss was negligible. How much loss would you expect across the 8-bit circuit?, I would assume it's double the 4-bit?

I don't think it will be enough to worry about, but without testing and prototyping there is no way to be 100% sure

With each stage you'll burn more power, yes, but you're not going to have trouble getting power to each consecutive stage. Each stage will actually amplify the signal, and each stage has it's own power and ground connections. So long as the output of the previous stage can supply enough to the next stage to saturate the transistor, you'll be fine. In this case, you're definitely ok. If you're worried about overall power usage, you can use 100k ohm resistors at the base and 10k ohm pull resistors. Output buffers will be needed if you want to drive LEDs very bright though, just connect the output you want to use to the base of an NPN transistor with a 100k ohm resistor and connect the LED directly from the collector and power pins (maybe put a 100ohm resistor in series with it to be safe, but it's really unlikely that you'll need it because the transistor will act like the appropriate resistor in this case).

Finally finished the project after almost 9 months. You could say it was my baby. More of a learning experience though than producing anything particularly useful. I'll post up some pictures of it when i get a chance but here's a video of it.

http://www.youtube.com/watch?v=_pUx1KDCPMo

Yep, there's an error in the video as i had a short somewhere down the line, but i've fixed that. The voltage drop when all stages were on ended up being around 0.3V or something like that but i'm not entirely certain as i discovered my multimeter was malfunctioning the next day and i haven't got around to testing it with my new one.

That's really cool You should show the circuit in the video as well as the finished result. I love the buttons which light up, it's a very nice touch.