eionmidi Posted April 16, 2008 Report Share Posted April 16, 2008 HiI am intending using the DOUT boards with MIDIO128 cores to drive stop tab magnets on my organ console. Past posts have tended to refer to pipe magnets (which draw less current) and the R3 version of the DOUT.In this post http://www.midibox.org/forum/index.php/topic,6530.0.html Smashtv says:'When loaded for relay drive the 2803's Vcc pin is brought out from each chip separately to it's respective output header. I figured the relay supply voltage would be near the devices to be driven rather than always near the DOUT itself. It's the one pin left unnamed on the J3-J6 connection silkscreen.'In the DOUT R4 board page there is a change: 'Isolated "spare" pads for driver chip loading to allow foreasy use with alternate drivers'Q1a - Does this mean that for the current R4 boards, populated with ULN2803, neither the GND (pin 9) nor the Common (pin10) of the ULN is now connected to anything? Q1b - The Vs pins on each of the J3 to J6 connectors are connected to the ground of the board but NOT the GND of the ULN chip?Q2 - If so, what is the recommended method of physically wiring to these two pins? In my wiring design, the GND will sink 2 amps (the maximum is 4A).A clarification of these points will be helpful to the small band of organ enthusiasts. Any comments from forum members who are driving pipe or stop magnets with this board and ULNs would be very welcome.Eion. Quote Link to comment Share on other sites More sharing options...
John_W._Couvillon Posted April 16, 2008 Report Share Posted April 16, 2008 Eionmidi, anybodyJust happens I have a question concerning driving pipe magnets with the ULN2803 on the DOUT card, so I will add my question to yours.At times, it is desired to drive two or more magnets from one ULN output combining two pipe ranks. In the past, this arrangement has caused problems, as one output conducting and the other output in the high impedence state has caused failure of the output in the high impedence state. Has anyone else experienced this? I propose to put two diodes in the circuit as shown on http://www.esnips.com/doc/d820e2bc-b950-4a22-bbeb-685ec2047d1a/PARALLEL-ULN-OUTPUTS-DRIVING-A-MAGNET. Hope the link works.Any comments, anybody?Johnc Quote Link to comment Share on other sites More sharing options...
John_W._Couvillon Posted April 28, 2008 Report Share Posted April 28, 2008 eionmidi,check out the link on my reply above to your post concerning douts. The link shows the connections to one ULN chip. I have added some diodes on the schematic to prevent any cross interference when more then one ULN drives the magnet. The diodes are not necessary, normally,and the magnet would be connected to one ULN.Johnc Quote Link to comment Share on other sites More sharing options...
eionmidi Posted April 28, 2008 Author Report Share Posted April 28, 2008 Thanks JohncYour diagram makes the circuit very clear.Eion. Quote Link to comment Share on other sites More sharing options...
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