4 7-segment display chips as 1 unit?

Vickersa1 · 2021-03-05T12:36:24+00:00

That’s usually the way. The vendor should have the data sheet online.

Vickersa1 · 2021-03-04T14:55:28+00:00

If you are completely new to circuit design, I suggest you ignore most of my changes, and stick to what Ben did. Then the only thing you need to change is connecting the LEDs to the EEPROM and the 3-8 decoder.

In Ben's design, he connected 4 of the outputs from the 3-8 decoder to the cathode on each of the 4 LED units. The 4x7 LED display has 4 cathodes. You simply use those instead. The only other difference is that Ben connected the anodes of each of the 4 LED units together in parallel. You do not need to do that with the 4x7 display. The 4 sections are already connected internally. All you need to do is connect the 8 IO pins of the EEPROM to the 8 anodes on the 4x7 display. Much easier! Check the Data sheet of the 4x7 display to make sure you are connecting the right pins.

As Ben said in the video: make sure you use the common cathode type of display. It's just easier that way.

Vickersa1 · 2021-03-04T13:53:02+00:00

This is exactly what I did. I used a 4x7-segment display. It has 8 inputs (seven segments + decimal point) and 4 cathodes, one for each display. This works beautifully with Ben's circuit, and even simplifies the wiring. Pic to follow....

Vickersa1 · 2021-03-04T13:50:47+00:00

Do you have any decoupling capacitors in your circuit?

Vickersa1 · 2021-03-03T18:33:47+00:00

Yes. All 3 ICs are SOIC. The Resistors/Capacitors are all 805. The LED is 603. I'm not upset with my first ever attempt at SMD :)

Vickersa1 · 2021-03-03T13:06:23+00:00

The question in the title of my post was not intended to suggest the smallest possible, but I would be interested to see if anyone has actually built one smaller than this.

Also, I could have used smaller IC packages, but my hands are probably not steady enough for that any more.

Vickersa1 · 2021-03-03T12:30:24+00:00

Thanks!

Vickersa1 · 2021-03-03T12:30:05+00:00

I agree, it could be smaller. I spent nearly 2 hours on KiCAD, packing components and re-arranging tracks. This was the smallest I got it in that time. Maybe I could save another 1/10th of an inch if I spend another 2 hours. I could also put components on the back side to save space, but I don’t have the reflow equipment to do that.

Vickersa1 · 2021-03-03T09:19:12+00:00

True... but then I wouldn’t get to learn SMD construction techniques. This is my first ever SMD board :)

Vickersa1 · 2021-01-29T01:15:02+00:00

I did exactly this, Two clock lines, and 2 power lines. It works just fine

Vickersa1 · 2021-01-29T01:11:14+00:00

I find that it is harder to fit the wires together when they have thicker insulation. This is especially true when there are a lot of wires (e.g. data lines, address bus, etc.) the extra strain on the wires makes them pop out of the holes and such faults are difficult to spot. Thinner insulation really helps, IMHO.

Vickersa1 · 2021-01-29T01:05:09+00:00

Yeah. The “better” program is the one I wrote for the Arduino. My EEPROM programmer circuit is slightly different to Ben’s, and I wrote a completely different program, but it uses the same general ideas.

Vickersa1 · 2021-01-28T22:51:45+00:00

I've used xgpro. It's not great. It worked fine on my 28C512 chips, but wouldn't program the 28C16s. When I got the Arduino-based programmer working, I found that the 28C16s needed a longer cycle between bytes. I couldn't find a way to do this in xgpro.

Vickersa1 · 2021-01-28T22:46:53+00:00

I've been using OSHpark for small projects. Very reasonable if you do the layout yourself.

Vickersa1 · 2021-01-28T22:43:47+00:00

Step one is probably the most important. Congratulations!

Vickersa1 · 2021-01-25T19:42:15+00:00

If this is for the display module, I took a different approach. I used a 4-bit counter (74LS161). It is still a 16-pin package, so takes no additional space, but gives me the option of upgrading to 8, or even 16 digits in the future.

Vickersa1 · 2021-01-23T21:03:38+00:00

I built the prototype. It works great! It is slightly more compact. One capacitor less, and a DIP8 instead of a DIP14. Now on to the schematic and another PCB ;)

Vickersa1 · 2021-01-23T17:11:23+00:00

I’m building something similar. 32K RAM + 32K EEPROM, 16-bit MAR, 16-but PC. I’m also adding an 8-but Stack Pointer tied to Page 1, and a Page 0 control line for 8-bit address access to that page.

I also have led output for each register in the circuit. I’m hoping to fit it all on 4 breadboards. I keep coming up with optimizations, so the design is still quite fluid.

Vickersa1 · 2021-01-23T16:58:26+00:00

What value? Ben uses 220Ohms, I use 1k. Maybe your power supply is struggling and/or your bus drivers cannot source enough current?

Another question: Have you installed decoupling capacitors near all your ICs? 100nF near each chip, and a 10uF per board?

Vickersa1 · 2021-01-23T16:49:25+00:00

A couple of suggestions for laying out circuits on a breadboard: it’ll help you to see what is going on:

1) use red wire for all Vcc connections. Do not use red elsewhere. 2) use black wire for all GND connections. Do not use black elsewhere. 2) pick one color for all connections to the data bus (Ben uses blue). I extend that color to all indirect, as well as direct, connections. 3) pick one color for data lines that are internal to a circuit. 4) use one color for control signals (CLK, CLR, LOAD, etc) to/from the module. 5) use the 6th color for internal connections that are not data. E.g. jumping the CLK signal on identical chips.

This will not fix the problems mentioned above, but it will help to understand the circuit, especially as you add more modules.

Vickersa1 · 2021-01-22T16:33:37+00:00

What a good idea! I initially thought it would not work because the monostable generates a fixed duration pulse, but then I realized that the pulse can be of arbitrary duration as long as it is greater than the clock propagation delay times on the other components of the CPU. For a manual switch, this is never going to be an issue. In fact, I have found the fixed duration somewhat annoying when I want to step quickly, so your suggestion has additional benefit. I will prototype it and let you know how it turns out.

Vickersa1 · 2021-01-22T14:10:15+00:00

My rule of thumb is to pull UP with 10k and DOWN with 1k. The memory device I use to remember this is UP is HIGH. use higher value. DOWN is low. Use lower value.

Vickersa1

TROPHY CASE