Showing posts from January, 2014

ALU Construction: Arithmetic Card Power Rails

Another round of soldering done ... this time putting down the power rails on the arithmetic card along with some soldered wire links. This is the last of the soldering for this card - it's all wire wrapping form hereon in.

The rear of the card now looks like this:
The power rails are very similar to the ones of the logic card completed earlier and they were just as fiddly to complete too ... although, that said, I do seem to be developing a bit of a 'sixth sense' for how long a wire should be cut without measuring it.

Additional to the power rails are the four soldered wire links on each arithmetic bit (totalling 32 links for the 8 bits in total). These would usually be wire wrapped on the top side of the board but are soldered on this side to free up some space for the other wraps needed.

Speaking of the top side of the board the only real difference from the last post is the additional set of header pins connected to the red power rail that will distribute power via wir…

ALU Construction: 1-bit Arithmetic Full Construction

So, as mentioned in my last post this time I've put in the wire links and wraps needed to test the first bit of the arithmetic card. With these in place I can make sure everything works as it should before repeating it all eight times over to make the full 8-bit adder.

As a quick reminder here's the diagram for the 1-bit full adder:
Reproducing this on the arithmetic card gives the following (on the front of the card):
and the following (on the back of the card):
To be able to test the circuit above I needed to temporarily hook up the positive and ground power (through 'cunning' use of crocodile clips) and then link up the Carry In, Input B and Input C. First time around I forgot about connecting the inverse Carry In as well as the regular Carry In so was getting odd results but with everything finally hooked up correctly everything works as intended.

Here's a picture of the circuit with relays inserted and inputs/power attached:
and another showing the whole arit…

ALU Construction: Arithmetic Card Relay Sockets

It's always a fiddly job getting the relay sockets soldered in and the ALU arithmetic card proved no exception. With this in mind I've been spreading the work out over several mini sessions in accordance with my new post-Xmas lack of patience. Therefore it's taken me a bit longer than it would otherwise to complete this stage of construction although to be fair I also got distracted with a Nixie clock kit my partner bought me for Christmas ... and I ran out of solder (this time though I've finally stumped up the cash to buy a 500g reel which should keep me going for a good while). Anyho, after much procrastination all the sockets (and diodes) are now on.

This time around I found that (mercifully) the sockets generally stayed in place whilst I soldered them which saved me holding the socket in place with one hand while dropping a solder blob to anchor one of the pins with the other hand. It seems that if you place the socket correctly first time it'll stay put but i…

ALU Construction: Arithmetic Card Header Pins

Following on from the successful construction of the ALU logic card in my last post it's time to start off the new year with the next ALU card (number 2 of 3 ALU cards in total) ... the arithmetic card. As for the logic card I'll begin by soldering down all the header pins that will be wire wrapped to later on (the LEDs and connectors were already added to this card earlier).

The construction method is pretty much the same as was used on the logic card although one oddity with this card is that the relays are placed in an offset back-to-back pattern to make some of the later wiring line up better. I soldered enough of these down on the logic card to get reasonably good at it and for the headers that don't sit still I've settled on soldering down one pin then adjusting (by re-melting the joint up and moving the header) and then finally soldering the rest of the pins.

Here's the result of this evenings work:
The next job ... which isn't all that much fun based on…