Jump to content

MIDIBOX CV - Higher Gate Voltage


bentron
 Share

Recommended Posts

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

Link to comment
Share on other sites

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

Link to comment
Share on other sites

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

Link to comment
Share on other sites

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

Link to comment
Share on other sites

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

Link to comment
Share on other sites

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

Link to comment
Share on other sites

  • 10 years later...

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
 Share

×
×
  • Create New...