Guest Mick Berg Posted March 2, 2007 Report Share Posted March 2, 2007 I want to use the SmashTV DIN board with +5v keying, ie 5v on the pin makes it go high.How do I modify the PCB so that the resistors are pull-downs instead of pull-ups? It seems that there are no "isolated red wires" like the older boards described in the instructions.Thanks,Mick Berg. Quote Link to comment Share on other sites More sharing options...
Wilba Posted March 2, 2007 Report Share Posted March 2, 2007 At the top of the board, pin 1 of the resistor networks and the discrete resistors are all connected by one track on the bottom. You can break it at the top left corner on the top layer and use wire between a pin connected to that track and a pin at ground.The bottom is a bit messier, as the same tracks carry 5v to the chips and bypass capacitors. Break tracks on the top layer to the right of C1, C2, C3 and below C4. Break track on the bottom layer between left resistor network pin 1 and J1. Now all those pull-ups are connected and separate from the pin 1 of the chips and you can wire then as pull-downs. But don't forget, you also need to wire the pin 1 of the chips together, and also to Vd of J2. Quote Link to comment Share on other sites More sharing options...
Guest Mick Berg Posted March 2, 2007 Report Share Posted March 2, 2007 Thanks for the advice. I wonder if there are any of the older boards available. Or maybe I should get some relays and leave the board the way it is, I have to deal with a 15volt keying voltage anyway.Mick Berg. Quote Link to comment Share on other sites More sharing options...
ReinerS Posted March 2, 2007 Report Share Posted March 2, 2007 Hi Mick,how exactly is your keying and voltage divider set up?You say you have a 15V keying system. Is there a well defined voltage any time (so it is switched between ground and 15V), or is it 15V when the switch is ON and OPEN (no defined voltage) when the Switch is OFF?In the first case, when it switches between 15V and 0V, you will only need your voltage divider (as you discussed in the other thread). There is no need for pullup or -down resistors on the DIN boards then. These are there to pull the inputs to 5V when the connected buttons are open (or no buttons connected). I'm not sure at the moment, but I think the behaviour of the 74HC chips is basically undefined with open inuts (please someone correct me when I'm wrong).Even in the second case, when you do have a complete voltage divider outside the DIN board, that would already provide the pulldown to ground when the switch is open. So you will only need the resistors on the board if you plan to use them as part of your dividers (in which case you would need a 30k resistor for the external ones).You should also be aware that the Midio128 software (and also the stuff I mailed to you) is programmed for negative keying, i.e. the switch is recognised as ON when the input level turns to zero. So you will have to change that in the software. (I think in the Midio128 you can do that with the sysex configuration that is provided to define all the messages).Reiner Quote Link to comment Share on other sites More sharing options...
Guest Mick Berg Posted March 3, 2007 Report Share Posted March 3, 2007 The switching is between ground and 15V, 15V when the switch is ON, and grounded when the Switch is OFF. I dived into this project without enough forethought. I realise now all the many things I did wrong, and I'm sure it will work next time!Thanks,Mick. Quote Link to comment Share on other sites More sharing options...
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