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strophlex

Midification of "family organ" rhythm unit

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Hi

I have recently got the idea of taking the analog pecussion part from the rhythm unit of an old half-working electric organ that I got for free and turn it into a midi controlled drum machine. I have ralized that the drums are triggered with 12V pulses and mixed and output as a -0.8/0.8V signal. It would be convenient to trigger the percussion via a DOUT module, but can it output 12V trigger signals? Also, what is standard line level and what would be the best option to amplify my output signal considering level and output impedance.

Thanks.

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I have been looking around a bit and found this relay http://www.farnell.com/datasheets/119542.pdf

The trigger signals of the rhythm unit use 0.8mA 12V so I think it would be enough. I don't really get how to control the relay. Is it triggered by a voltage or a current? Do I have to place a current limiting resistor between the second input pin and ground like this?

+5(shift reg out) --- (pin1 relay pin2) --- resistor? --- gnd

Is it possible to drive these relays directly from the shift registers? Can they deliver enough current, how much current is needed? I find the data sheet a bit cryptical. As you see I am a bit confused here. I don't even know if I put this in the right section of the forum :P

Thanks for any help

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After some talk to lylehaze I have decided to trigger the drums with a comparator cirquit made up of two TL074s. I will post a few updates as the project progresses for dokumentation.

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I got sound from the drum unit triggering it with the comparator. I use a modified atx psu so i get some low frequency noise, probobly from the fan or something else carried in the supply voltage. I will try to filter it with some caps but anyway, I will not use that psu once i am finnished. I tried to twitch some pots and could modify the snare drum in really cool ways, so I will probobly replace the trim pots with panel pots :)

Next step is etching a core pcb and build it, connect all the drum triggers and hook them up to both tl074's. Borrow a shift register from the allmost complete mb6582 to the DOUT and make the code which seem to be simple enough.

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Now I got it all hooked up and can play the individual drums from my master keyboard via midi. Everything worked as I expected and writing the code was a really simple task. I attached a diagram of the circuit. J1 is the connection to the DOUT interface of the core and J2 is the trigger connections to the drum circuit.

untitled.GIF

untitled.GIF

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Nice one!

and thanks for sharing the schem!

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Very cool!

I've got some old drum machines (MiniPops & Hammonds etc) that I'd love to give this similar treatment, but the programming has sort of scared me away.. listening to that has inspired me to give it a go.

Regards

Mike

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Here is a short audio sample.

Niiiiiice!  And thanks for the schems too!  I have an old Arista boomp-chikka preset rhythm box I want to give the same treatment - all discrete components inside so ripe for modding. 8) Have you got any thoughts on modding yours? 

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Thanks for the response!

I stared off measuring voltages on all interconnections to the board I wanted to use. I measured dc with a multimeter and ac with a soundcard oscillocope while a rhythm was playing, made notes of all measurements. Then I grounded the pins that seemed like ground from the measuring briefly with an aligator cliped wire with the intension to see if anything was lost from the sound. Some pins changed voltage on drum triggering so after trying to measure these voltages I tried to trigger them myself with a dc supply and aligator clip. It worked :) When I felt sure of the connections I desoldered the ones that seemed unnecessary and made sure it still worked in the organ. Then I took the board out and tried to make it alive on my lab bench. Then I dessigned the circuit.

I didn't know were to start with the design, but asking around payed off and the comparator solution was deffenetly the way to go. The code was really simple (ask me to have it). I looked at the "lighting leds" example available at ucapps. The only problems I have had was missing to connect a ground wire and since I looked for other error sources it took some time to fix it. I did it twice too  :-[

The next step is designing a psu (will hopefully get rid of the background noise) and making a pcb for the comparator circuit and the psu.

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