bentron Posted September 10, 2007 Report Share Posted September 10, 2007 Hi there,i´ve just completed my midibox cv and it works really good. But i have one (maybe stupid) question regarding the gate voltage:I need to have a higher gate voltage than 5V, because i have a Roland SH-1 Synth wich doesnt react to the gate signal from the box, so i read the manual and noticed that it starts triggering at about 7,5 V.So is it possible to increase the gate voltage? i mean, i did a previous project where you could just increase the circuit supply voltage to increase the gate voltage. but i have doubts that this will also work in this case.And since i am pretty new to electronics, i will not try it either :)I´m using the AOUT Version, so maybe there is an option to increase the voltage only for the 2 gates provided by the AOUT?Thanks in advance for your suggestions!greets, bentron Quote Link to comment Share on other sites More sharing options...
seppoman Posted September 10, 2007 Report Share Posted September 10, 2007 Hi,the gate voltage can´t be increased directly on the AOUT. But you can use an ULN2803. This is a driver IC which takes up to 8 logic inputs and drives corresponding outputs from a separate supply voltage (e.g. 9 or 12 Volts). This is a quite simple cirquit that can be built easily on vectorboard.Seppoman Quote Link to comment Share on other sites More sharing options...
bentron Posted September 11, 2007 Author Report Share Posted September 11, 2007 hi seppoman, thanks for your response.i picked up a ULN2803 today and just connected it like described in the datasheet - means i didn't use any additional components, just the ic. That didn't work and now i have a big problem: the gate port i connected to the ic is dead - it produces a constant voltage between 1,7 and 2,5 volts and doesnt react to midi messages anymore - did i destroy the pic? ??? ??? i'm sure i had the right pinning on the ic but should i have used any additional components? and is there any possibility to get the gate port back working? i thought of replacing the software in the pic - i´ll try that and post the results.any additional suggestions wuold be great.thanks & greets,bentron Quote Link to comment Share on other sites More sharing options...
stryd_one Posted September 12, 2007 Report Share Posted September 12, 2007 Bentron you should search here and the wiki and also look on smashtv's site for information about these IC's. I don't know anything of them personally but I know that this has been done before. Quote Link to comment Share on other sites More sharing options...
seppoman Posted September 12, 2007 Report Share Posted September 12, 2007 Hi,that doesn´t sound very good. First of all, do you use the AOUT_LC or AOUT, the gate outputs from the AOUT or from the core? From what PSU did you power the ULN? I hope it was a regulated DC one? As you can see e.g. on the DOUT page of SmashTV (http://www.avishowtech.com/mbhp/mbhp_doutR3.html), the ULN can be used without any additional cirquitry - just +VCC on pin 10 and GND on pin 9. Then just take two inputs and you get the higher voltage on the corresponding outputs (e.g. pin 1 and 2 control pin 18 and 17). BTW: I suppose it´s neccessary that both the ULN and the rest of the cirquit do use the same ground level also to prevent any uncontrolled currents flowing over the logic connection. If you´re using some integrated +´5V, +-12V PSU, there´s no problem. But if you used a separate PSU for the ULN, you need to solder a wire between the ULN (new PSU) ground and the regular midibox ground.First and most important you need to get things working again without ULN. If it´s an AOUT, I hope you didn´t somehow fry the DAC ICs. Do they still output CV voltages?Seppoman Quote Link to comment Share on other sites More sharing options...
bentron Posted September 12, 2007 Author Report Share Posted September 12, 2007 Ok, i'll try to describe the problem as precise as possible:I'm using an AOUT and the dac's are still working. means i have correct cv voltages on all eight channels.Also all gate channels are working except channel 4 wich is the one i connected the ULN to. It doesn't react to any midi messages and outputs a constantly varying voltage between about 1,5 and 2,5 volts (i measured directly on the corresponding pin at j5, to sort out possible shorts at the jack sockets and wires). I connected the ULN exactly as described, i just used some wire for testing purposes and connected pin 9 and 10 to ground and +12v and then wired the gate out to pin 1 measuring the voltage at pin 18. When i didn't mesure anything, i double checked the connections to the ic, but everything ok. i measured every pin of the ULN while connected, when i noticed the gate output was dead.Interesting thing is: the (broken) gate delivers, as described above, a constant gate voltage about 2v. when i reconnect the ULN to the broken gate, the voltage drops to 0v. ??? ??? So all in all it's "just" gate channel 4 thats affected, everything else works properly.greets, bentron Quote Link to comment Share on other sites More sharing options...
stryd_one Posted September 13, 2007 Report Share Posted September 13, 2007 So all in all it's "just" gate channel 4 thats affected, everything else works properly.If we rub your belly like Buddha, will some of that amazing luck be passed onto us? :) Quote Link to comment Share on other sites More sharing options...
bentron Posted September 15, 2007 Author Report Share Posted September 15, 2007 ok, the box works again. i fried the pic :-[ seems like i shortet the gate pin somehow while testing the gate driver ic. however, the friendly guys in the chatroom ;D told me to use the udn2981 8 Channel Source Driver IChttp://www.pescadoo.net/annexe/simda/chips_data_sheets/UDN2981.pdf to increase my gate voltage. i got one of them yesterday and it works perfect. :D no additional circuitry required, just connected it like described in the datasheet.thanks alot to all of you for the fast support!greets, bentron Quote Link to comment Share on other sites More sharing options...
stryd_one Posted September 15, 2007 Report Share Posted September 15, 2007 Glad it works! Thank you for documenting your solution :) Quote Link to comment Share on other sites More sharing options...
Alasdair Moon Posted September 19, 2017 Report Share Posted September 19, 2017 Now this is handy to know .... building my CV breakout I was asking myself if the 4.8V Gates and triggers are enough for my +-15V modular. Quote Link to comment Share on other sites More sharing options...
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