[sdiy] (OT) Doepfer MIDI-CV oddity

[Ullrich Peter]

Hi!

If you have a look at different circuits on the net you can find different values:

The highest values I have seen were 4k7 (which was too high for all my different types from Sharp to Toshiba).
Some use 2k2, some 1k and the lowest value I have seen was 220R.  I had luck with 1k downto 220R but use normally 1k because with 220R the supply current is higher than with 1k and I got the same results.

220R pullup: If you have Uce-saturation voltage with about 0.4V you get nearly 21mA current when using 5V supply voltage against 4.6mA when using a 1k pullup.

For the bias resistor I found: no resistor (leads to slow rising edges on the output) / 10k or 15k (no big difference between these two - both useful).

Ciao
Peter

-----Original Message-----
From: synth-diy-bounces at dropmix.xs4all.nl [mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of Steve Ridley
Sent: Wednesday, January 19, 2011 2:19 PM
To: synth-diy at dropmix.xs4all.nl
Subject: Re: [sdiy] (OT) Doepfer MIDI-CV oddity


I've seen a similar problem which I solved with a pull-up in the midi out circuit.

The output device was just open collector TTL gate with an output resistor, and I don't think it was shutting off efficiently, any leakage current etc being pulled through the opto at the Midi In end. I added an extra pull-up resistor - a few K, can't remember exact value - between the open collector output pin and +5v - and it cleaned the signal up nicely.


Steve



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