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 Forum index » DIY Hardware and Software » Lunettas - circuits inspired by Stanley Lunetta
"SystemTechnik Digital Experimeter" where to start?
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okelk



Joined: May 08, 2014
Posts: 29
Location: Vienna

PostPosted: Mon May 26, 2014 10:41 am    Post subject: "SystemTechnik Digital Experimeter" where to start?
Subject description: how do I get this thing to oscillate?
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Hi!
I recently got two suitcases with educational digital logic experimenting kits.

They are called "SystemTechnik Digital Experimeter 1" and "SystemTechnik Digital Experimeter 2"

They are based on 7400 series logic chips.
I haven't found out yet which kind of connectors to use....maybe 2mm bananas, but my calipers are to big to messure the holes...

I am kind of new to lunetta synths, but I understand the principles of digital logic and I played arround a bit with 40106 oscillators.

Where should I start to get an oscillator using these 'digital experimenters'??
(possibly without altering the case?
Can I use two of the 4-input nand gates ( 7420 ) to form an oscillator (maybe with resistors/potentiometers build into the cables)??

where would you start? got any ideas on how to use this stuff?

I added just 1 picture...can take more (also from inside) if anybody is interested...


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Tycho Brahe



Joined: Apr 24, 2014
Posts: 5
Location: Cologne Germany

PostPosted: Mon May 26, 2014 7:09 pm    Post subject: Reply with quote  Mark this post and the followings unread

Nice cases!
AFAIK in this forum everything is about the 4000 series, but I have seen videos on youtube about logic synths using the 7400 series, so it is possible.
But a 4 input NAND gate isn't very useful for an oscillator, a Schmitt trigger would be the easiest way to build it.

Another possibility: the ICs are placed in sockets if i see it correct, so you can easily replace them with the 4000 series, but you maybe will need to change the circuits on the pcb as well (replacing resistors, changing supply power...)
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DUBmatze



Joined: Feb 18, 2013
Posts: 113
Location: south Germaica (schwabilon)

PostPosted: Tue May 27, 2014 5:02 am    Post subject: Re: "SystemTechnik Digital Experimeter" where to start?
Subject description: how do I get this thing to oscillate?
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okelk wrote:
Can I use two of the 4-input nand gates ( 7420 ) to form an oscillator (maybe with resistors/potentiometers build into the cables)??

where would you start? got any ideas on how to use this stuff?
Hey, cool cases.
I would try first this circuit. its easy to build this as freeform circuit, just solder up and some heatshrink over the joints.

You can also try to short all inputs of the nand gate together (so you dont need a V+ outside)

I think the jacks are called "Märklin" or "2mm Zwerg" in german.


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PHOBoS



Joined: Jan 14, 2010
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PostPosted: Tue May 27, 2014 8:03 am    Post subject: Reply with quote  Mark this post and the followings unread

That looks very nice, should be useful somehow. Very Happy

Tycho Brahe wrote:
Another possibility: the ICs are placed in sockets if i see it correct, so you can easily replace them with the 4000 series, but you maybe will need to change the circuits on the pcb as well (replacing resistors, changing supply power...)

That's what I would probably do aswell. But you'll need to add pulldown resistors to most of the inputs. I see a bunch of resistors in there already
but for TTL they could be pullups for open collector outputs. An of course you have to check the pinlayout to see if you can just replace them or
have to do some rewiring.

DUBmatze wrote:
I would try first this circuit. its easy to build this as freeform circuit, just solder up and some heatshrink over the joints.
Posted Image, might have been reduced in size. Click Image to view fullscreen.
You can also try to short all inputs of the nand gate together (so you dont need a V+ outside)


The 7420 isn't a schmitt trigger NAND so that's not gonna work, however if you replace them with the 7413 (dual Schmitt trigger 4-input NAND gate)
then that is an option. You can do it with 2 NAND gates using a setup like here. Or if you don't mind drilling holes in the panel you could just add some extra oscillators to it.

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okelk



Joined: May 08, 2014
Posts: 29
Location: Vienna

PostPosted: Tue May 27, 2014 8:44 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks! I think they really are those so called 'zwergstecker' I think I will get a few at a local model railway shop to try out and be shure before I order more.

I also really like the pcb mounted banana plugs used on this thing. they seem to be acheap alternative to other plugs...anybody know where to get those?

PHOBoS wrote:

The 7420 isn't a schmitt trigger NAND so that's not gonna work, however if you replace them with the 7413 (dual Schmitt trigger 4-input NAND gate)
then that is an option. You can do it with 2 NAND gates using a setup like here. Or if you don't mind drilling holes in the panel you could just add some extra oscillators to it.


jep....didn't work.
I like the idea of using a 7413, but it seems to be obsolete...and quite expensive on ebay...is there a cmos alternative?
There also seems to be a 7418 " dual 4-input NAND gate with Schmitt trigger inputs" but I can't find it anywhere....

I looked into the possibility of using 2 nand gates for an oscillator....but it seems to take a lot of space if I want to leave the front panel unmodified.

hm...maybe its the best to build a external box with a few 40106 oscillators....I could still power it of the 5v from the case....

anybody got more ideas on how to use 4-input-nands in a patch?


Also it seems that the internal oscillator of this thing (fixed outputs up to 100hz) is using a 74132 quad 2 input nand with schmitt triggers. which is then devided by 7490 decade counters.... maybe it is possible to get the "master clock" to oscillate at higher frequencies....
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PHOBoS



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PostPosted: Tue May 27, 2014 9:58 am    Post subject: Reply with quote  Mark this post and the followings unread

okelk wrote:
Thanks! I think they really are those so called 'zwergstecker' I think I will get a few at a local model railway shop to try out and be shure before I order more
.
maybe bring it with you so can test right away if they fit, they could be 2mm instead 2.6mm.

Quote:
I like the idea of using a 7413, but it seems to be obsolete...and quite expensive on ebay...is there a cmos alternative?
There also seems to be a 7418 " dual 4-input NAND gate with Schmitt trigger inputs" but I can't find it anywhere....

I don't think there is a CMOS version of a dual quad input schmitt trigger NAND, just a standard one (CD4012) but it's not a drop in replacement for
the 7420 (different pin layout). I wonder what the difference is between the 7413/7418, I guess I should check the datasheet.

Quote:
Also it seems that the internal oscillator of this thing (fixed outputs up to 100hz) is using a 74132 quad 2 input nand with schmitt triggers. which is then devided by 7490 decade counters.... maybe it is possible to get the "master clock" to oscillate at higher frequencies....

unless it uses a crystal (I don't see one on the photos) that should be pretty easy to do. It's probably an RC oscillator so reducing capacitor
and/or resistor value(s) should give you a higher frequency. Also that 'thing' next to the oscillator looks like it could could be patched up as an
oscillator aswell. If I'm correct it gives a pulse of which you can select between 4 different lengths (time). So patching the inverted output to
the input (or output to inverted input) should make it oscillate.

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okelk



Joined: May 08, 2014
Posts: 29
Location: Vienna

PostPosted: Tue May 27, 2014 10:54 am    Post subject: Reply with quote  Mark this post and the followings unread

I couldn't get that thing to oscillate yet...
but it seems to be a pretty interesting chip. its a 74121 monostable multivibrator. the different outputs are just the chip hooked up to different capacitor values.
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richardc64



Joined: Jun 01, 2006
Posts: 614
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PostPosted: Tue May 27, 2014 12:17 pm    Post subject: Reply with quote  Mark this post and the followings unread

To get non-schmitt gates or inverters to oscillate you have to use two of them. Unused NAND inputs should be pulled up to +V. If thru a resistor, applying a low to the input will stop the oscillator: if the first gate is pulled low the oscillator output will also be low. If the second gate is pulled low the output will be high.

NORs can also be used. In that case unused inputs should be held low, or tied together. It's difficult to pull TTL inputs low thru any resistance greater than about 470 ohms, though. However, if you're really hankering to convert it all to CMOS, 74HCTxx has the same pinouts as 74xx, is input-output compatible, and can be pulled down -- if needed -- as easily as CD4xxx. Not all 74xx functions are available, though.

74xx can also be replaced with 74LSxx for lower current comsumption. 74LSxx inputs, however, are just as hard to pull down as regular 74xx.


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DUBmatze



Joined: Feb 18, 2013
Posts: 113
Location: south Germaica (schwabilon)

PostPosted: Fri May 30, 2014 1:27 am    Post subject: Reply with quote  Mark this post and the followings unread

PHOBoS wrote:
The 7420 isn't a schmitt trigger NAND so that's not gonna work
uuuupppps
Shocked

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