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Old 13th May 2018, 4:26 pm   #56
kan_turk
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Join Date: Mar 2014
Location: Dublin, Ireland
Posts: 396
Default Re: MK14 schematic revisions

Quote:
Originally Posted by Slothie View Post
Yes. a guy in California was selling them (I think it may have been the one you pointed out) so I bought 4. They arrived Thursday! So I have those and some 65X61 chips, and there is a link on the bottom of the board to select which type (they all have to be the same type).

If John can find his 7408s then I have a source for all the chips!
I just need to get my PROMs programmed; I have the schematic for the MK14 prom programmer, which I could hook up to an arduino. I just need to be sure it works first time because I only have the two!! Did I see you say you had a 74S571 programmer? could I ask you to program them for me if I sent you the PROMS and return postage?

The 7408 has a 130 ohm resistor in the output (see schematic) which would limits the current through the LED to about 25ma, which multiplexed 8 ways is an average of ~3ma which is the correct sort of average current for the LEDs in the bubble display.
Hi
Just to let you know - after a bit of archaeological excavation in what I laughingly call my stores, I located the 7808s
If you pm me your postal address and let me know how many you require I'll send them on their way - I'm still surprised that I found them as well as other long forgotten 'treasures'

Kindest regards
John
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