Open Cockpits Display Card.

[droddis]

I'm looking at using the open cockpits display card, does it matter whether i buy 7 segment common anode, or common cathode displays.

As the common anodes are only 30p each including delivery.

Thanks

[wanderer]

Yes, it DOES matter.

The Display Card II uses the common NEGATIVE (cathode) GROUND to trigger a change in display. All other segment pins receive +5 volts. So you'd be running the LEDs with reverse polarity. And since the D in LED is diode (which only passes current in one direction), you would get no display at all.

You CAN get cheaper common cathode LEDs (say on eBay) but if the pinouts are different than the OC ones, then you can NOT use the OC display PCBs.

[droddis]

Thanks, Do i need to use the opencockpit pcb holders or can i just connect directly to the 7 seg.

Thanks
David

[Trevor Hale]

You could connect direct to the 7 Segments, however it will be a wiring mess. The headers they supply will via PCB connect all a's, b's, c's etc. Saves a lot of wiring, time and effort. I strongly suggest you use the boards they will supply.

I went away from that route, and wish that I had not.

Trev

[wanderer]

You do not need to use a PCB holder at all but you will need a method of holding your digits in place (and aligned) and then need to connect (for example) all the Pin 1s together, then all the Pin 2s, etc. (Here's an an OC tutorial) So the wiring can get messy quickly.

Also, if you do not use LEDs with the same pinouts as the OC ones, then you will need to do wiring manually. I've been trying BPS "ziz-zag" boards which can be used to help connect all the "required" pins together. Then you will have to modify the board to separate the cathodes (since they too will be connected together).

"BusBoard-3U has a zig-zag circuit pattern that allows opposite sides of an IC or connector to be on the same or different traces. ICs and headers can be connected pin-to-pin without any extra wires or jumpers." So in the case for OC, you need to choose the correct starting column of pins so that all the pin 1s are on the same trace, etc. but with pin 10 -- the opposite side -- connected to a different trace.

[droddis]

So the display card can control 16 seven segment displays.
i wire all the pins together for the displays a to g and place the individual cathodes to the connector from 1 to 16. so the display for the comm freq will take up 4 segments if the first digit "1" is fixed through a resistor.

Also do the displays take there power from the display card or do i have to provide a seperate power source.

David

[wanderer]

Yes, I've found that I can't get the Displays lit up WITHOUT external power.

Also an update, the BPS ziz-zag board works well for (cheap) non-OC LEDs from eBay.

The LEDs I got had common cathodes on pins 3 and 8 (instead of 5 and 10 for OC-supplied ones) so the PCBs I bought from OC didn't work for me. (So the PCBs up in the for-sale forum now. Live and learn.)

Instead of messy wiring, the A-F segments are wired just like the OC PCB with a single 7 or 8 pin ribbon cable. All the common pins/segments (i.e A's, B's,...) are connected by the BPS board itself. Then I had to sever the traces for pins 3 and 8 on the BPS board with a dremmel tool. Followed by manually connecting the cathodes for each digit to the Display II card.

A caveat for beginners, get the USB expansion card. A USB-LPT cable didn't work for me. (More $ wasted.) Furthermore, I wasted a few day trying to diagnose a Display problem. (The SIOC server didn't really like using the LPT port and updated the wrong digit on occassion.)

[droddis]

With the common cathodes do you just connect the two pins to the display card so pin 3 and 8 would go to output 1 on the display and so on.

Thanks David

[wanderer]

I hope I understand your question....

My LEDs have cathodes at pins 3 and 8. Using IOcards, each segment pin ARE connected together. I run ONE 8-pin ribbon cable between the DisplayCard II and the ziz-zag board (matching pins with segments).

But the cathode of each digit must NOT be connected together so I cut the traces between each digit for pin 3 and pin 8.

Then I run 1 wire for each digit from the (16) Displaycard II output pins to pin 3 (or pin 8, only one pin needs to be connected) of the desired digit. (For example, pin 0 from displaycard II to pin 3 of the right-most digit.)