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space1649 / 8-bit-SAP-Breadboard-Computer-by-Space-Man

This is my build of Ben Eater's 8-bit breadboard computer
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Capacitors #2

Open DotTech opened 7 years ago

DotTech commented 7 years ago

I'm also building a SAP-1 using the instructions from Ben Eater.
With about 60% done, I'm running into some issues with voltage drops across the breadboards. I see that you have added a number of capacitors across several powerrail points. Could you elaborate on those? They are not mentioned in your schematic.

I have also added some capacitors now which seem to smooth out the DC signal (i.e. remove the ripple) but it's not doing anything to counter a significant voltage drop. What I mean by that is, when I connect power to the top-left corner of the SAP, voltage will have dropped like 1.5V when I measure it in the bottom-right corner. This results in parts of the computer failing, for example the registers. When I connect power somewhere in the middle of the SAP, everything works fine.

It's worth mentioning that I did connect all the power rails using 22 gauge jumpers, like you and Ben did.

loneregister commented 7 years ago

Hi DotTech - I found that picking up a powersupply 0-30V/0-5A, resolved the issue - I now get 4.5V across the whole breadboard. (I also soldered power rail wires in a bus with pins for the whole thing)

It seems that while the USB powered alternative is cheap and quick, we need a bit more ooomph to stay away from deep voltage sags.

p.s. when I was using the usb method, I too was experiencing the exact same problem, and would get down to 3.2-3.5V in places which did cause problems.

DotTech commented 7 years ago

I'm using a bench power supply that supplies up to 5 amps, but it's only pulling around 300-500 mA at the moment (the CPU is not complete yet) I will also try to apply the extra power rails like in the picture, maybe that helps.

Any tips on where to place capacitors and what values to use? I spread out four 47 uF capacitors out over the cornes at the moment.

loneregister commented 7 years ago

Not sure about the Capacitors. What I did was use some of the male pins and broke them into pin groups of two. Then I placed the two pin "headers" into the power rail on each breadboard, and then ran a red wire along each header pin,and soldered it on. I then did the same thing for ground. This way, power and ground coming from the supply, don't have any resistance by having to travel through breadboard friction connections. This solved my voltage drop problem as I got farther from the power source. It did not solve the problem that I was only getting 3.5V out of my USB supply. The Bench supply immediately put everything at 4.5V, which solved lots of weird intermittent problems.