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 Forum index » DIY Hardware and Software » Ken Stone designs - CGS
CGS10 mini keyboard expand to 32 keys
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Werebear



Joined: Nov 23, 2009
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PostPosted: Fri Jan 12, 2018 10:04 am    Post subject: CGS10 mini keyboard expand to 32 keys
Subject description: 74c922 datasheet expansion to 32 keys possible with Kens design?
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Hi

I've been looking at CGS10 mini pedalboard/keyboard schematics using (MM)74c922 that gives a sixteen key keyboard with CV and gate outputs. According to the data sheet the 74c922 can be expanded to 32 key input using a four input NAND gate, diodes and pull up resistors. However, I can't see how the second keypad switches or more precisely what it switches between.

There is probably a simple answer that I am unaware of but there seems to be nothing to switch between on the second keypad shown in the datasheet unless they connect to X1 to X4, which is not shown. It may be that that connection is implied but I don't know enough to be certain.

I have ten of these chips winging their way from China (£7.odd including P&P) so will be able to experiment soon and hopefully be able to produce 32 key keyboards/control surfaces for future projects.

Sorry to post the entire datasheet as I couldn't see how to extract the desired schemo.

Thanks

Jim


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Werebear



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PostPosted: Fri Jan 12, 2018 10:18 am    Post subject: Image from 74c922
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This is the schematic from the datasheet that I want to use but there appear to be connections missing.


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PHOBoS



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PostPosted: Fri Jan 12, 2018 11:11 am    Post subject: Re: CGS10 mini keyboard expand to 32 keys
Subject description: 74c922 datasheet expansion to 32 keys possible with Kens design?
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Werebear wrote:
..unless they connect to X1 to X4, which is not shown. It may be that that connection is implied but I don't know enough to be certain.

without really looking into it that would be my guess. I think I have some of those chips too, maybe I can do some experiments.

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Werebear



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PostPosted: Sat Jan 13, 2018 4:18 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks PHOBoS. Hopefully mine will arrive before too long and I can play with them to see how this works.

I think part of the problem is not understanding the conventions of schematic drawing, particularly digital stuff where some connections are not shown. I've studied electronics at college and university but that was a LONG time ago and now with synth DIY I'm teaching myself (mostly) analogue electronics a bit at a time through a senior haze. Such fun!

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gasboss775



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PostPosted: Sat Jan 13, 2018 10:32 am    Post subject: Reply with quote  Mark this post and the followings unread

The X outputs are definitely meant to be extended down to the bottom grid of 16 switches. It is very annoying when things like this are assumed ( by the writer ) to be implicit. Causes a lot of grief during the earlier stages of the learning process and sometimes even to those of us longer in the tooth with our hobby.

Werebear thanks for posting this, I reckon it will come in useful at some point as I have one of these 74c922 chips laying around somewhere.
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Werebear



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PostPosted: Sun Jan 14, 2018 4:41 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks GASBOSS for pointing that out. I was kinda sure that's what was going on.

When my chips arrive I'll have a play and post the results.

And still learning all the time!

Thanks.

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gasboss775



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PostPosted: Sun Jan 14, 2018 7:23 am    Post subject: Reply with quote  Mark this post and the followings unread

Werebear wrote:
Thanks GASBOSS for pointing that out. I was kinda sure that's what was going on.

When my chips arrive I'll have a play and post the results.

And still learning all the time!

Thanks.


You're welcome.

Are these still being sold? If yes can you tell me where?
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Werebear



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PostPosted: Sun Jan 14, 2018 10:47 am    Post subject: Reply with quote  Mark this post and the followings unread

After a few searches I found them here:

https://www.ecrater.co.uk/p/25678197/10pcs-ic-mm74c922n-mm74c922-fsc

But they may be on Ebay. I had no luck with RS, Rapid, CPC, Mouser et al and googling for replacement chips didn't find anything suitable or I would know how to use!

I've just noticed that actually I paid £5 for delivery so total is more like £12.odd but that's for ten IC's. Suppose it will be different if you're not in the UK.

By the way have just checked the page and they claim to have only one available.

Jim

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gasboss775



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PostPosted: Sun Jan 14, 2018 11:24 am    Post subject: Reply with quote  Mark this post and the followings unread

Werebear wrote:
After a few searches I found them here:

https://www.ecrater.co.uk/p/25678197/10pcs-ic-mm74c922n-mm74c922-fsc

But they may be on Ebay. I had no luck with RS, Rapid, CPC, Mouser et al and googling for replacement chips didn't find anything suitable or I would know how to use!

I've just noticed that actually I paid £5 for delivery so total is more like £12.odd but that's for ten IC's. Suppose it will be different if you're not in the UK.

By the way have just checked the page and they claim to have only one available.

Jim


I reckon there's a good chance they could be fakes particularly at that price for 10. This doesn't necessarily mean they won't work, but they might not be quite up to spec. I got a new old stock RS part of eBay a couple of years ago.

The brand mark is for Fairchild and according to their website they don't make these chips anymore. I did find a Fairchild datasheet from 1987 for this chip on one of those sites that specialise in old datasheets.
The Chinese make copies of many obsolete chips, sometimes successfully sometimes not.

It's a good bet that if the manufacturer's website no longer lists the part that it could be a fake. I wish you good luck. Let us know how you get on with them, Ive had some good luck with fakes and a lot of the Chinese ebay sellers have free postage included in the deal so it can be worth the gamble!
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Werebear



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PostPosted: Sun Jan 14, 2018 11:52 am    Post subject: Reply with quote  Mark this post and the followings unread

To be honest those are actually my thoughts but my experience is that I haven't been burnt yet! I've had CA3080s from China that friends told me wouldn't work work very well in T.H.s VCO 1 - the first VCO I've been able to build with a repeatable scale that I could actually play a tune on - and if the specs aren't quite there then the sounds coming from my speakers are far too exciting for me to care right now.
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