Maybe TOO simple ? - Page 1
Forum section: electronics / beginners

author: KermitDK
author_rank: Unknown
timestamp: February 26, 2016, 09:54:12 pm
content: Hi,I am really stuck (or tired) :I have a 0 to 10 V DC signal, and I need to convert it to a -5V to +5V signal.Any ideas ?BrClaus

author: Pack34
author_rank: Frequent Contributor
timestamp: February 26, 2016, 10:15:50 pm
content: What available power rails do you have?

author: Andy Watson
author_rank: Super Contributor
timestamp: February 26, 2016, 10:35:06 pm
content: Need some more information - like what is the source of your signal and what is it destined to drive. A quick and dirty solution would be to stand the signal source ground on a reference of -5V - but we would need to know more details to determine if this is an acceptable solution.

author: uncle_bob
author_rank: Unknown
timestamp: February 27, 2016, 01:03:24 am
content: HiAs mentioned before, we're making guesses on to little info.Wire up an op-amp with a +/- 12 V supply. Feed the 0 to 10 into one input. Bias the other at 5V with a pair of resistors. The output will swing +/- 12V. Attenuate it to +/-5 with another pair of resistors.There are maybe a few thousand other ways to do it. The one above is pretty much guaranteed to be right in one individual case and utterly wrong in a few thousand other cases.Bob

author: Phoenix
author_rank: Frequent Contributor
timestamp: February 27, 2016, 08:46:51 am
content: Quote from: uncle_bob on February 27, 2016, 01:03:24 amHigh pass filter/AC couple it with a series capacitor is my though on one of many thousand ways...

author: KermitDK
author_rank: Unknown
timestamp: February 27, 2016, 08:51:58 am
content: Yes it was very little info - sorry for that :-)Let me explain :I have a Moog Slim Phatty synth module and a Arturia Beatstep Pro sequencer.The problem is that the Moog needs a -5 to +5 V to control the pitch, an the Arturia sends 0-10 V. (1V/Octave)(So much for standards).I know : "Why do you not just use MIDI ?" - Answer : "At some point I will not be able to use MIDI, so I can just as well solve the problem now" :-)Regarding voltages, I haven´t taken the Moog apart yet, to see what voltages that are available on that, but if nothing suits - I´ll just make what is necessary.

author: uncle_bob
author_rank: Unknown
timestamp: February 27, 2016, 01:08:49 pm
content: Quote from: KermitDK on February 27, 2016, 08:51:58 amHiOk, you have a continuous control signal out of one box and you want to put similar range signal into the other box. The quick/ dirty offset the grounds probably is not going to work. An op amp or two is probably the best answer.One of many ways to wire it up:0 to 10V signal goes to two 10K resistors in series. Other end goes to ground. Center tap goes to the + input on the opamp. Another 10K goes from the opamp output to the - input. You can either use another fixed resistor or a 20K pot to the B+ supply to get the correct offset. Given that the 0-10 on one end may not really match up with the -5 to +5 on the other ... I'd go for the pot.Bob

author: Zero999
author_rank: Super Contributor
timestamp: February 27, 2016, 02:43:47 pm
content: Here's one way. The op-amp isn't too critical, the uA741, LM358, TL072 etc. will do.It doesn't need a -5V reference: the LM79L05 will do.

author: uncle_bob
author_rank: Unknown
timestamp: February 27, 2016, 03:58:40 pm
content: Quote from: Hero999 on February 27, 2016, 02:43:47 pmHiA low-ish value pot or pair of resistors off the -9V supply will do a pretty good job of replacing the 5V ref as well. That assumes that the supplies are regulated.Bob

author: KermitDK
author_rank: Unknown
timestamp: February 27, 2016, 06:03:35 pm
content: Thanks to all :-)That will be tested tomorrow.I took the Moog apart, and there is a +/- 15 V and a +/- 5V rail, so it should be possible to make it work.(I´ll use a 7809/7909 for the LM358)BrClaus

author: Zero999
author_rank: Super Contributor
timestamp: February 27, 2016, 06:21:33 pm
content: Quote from: KermitDK on February 27, 2016, 06:03:35 pmThat's good but why not just run the LM358 straight from +/-15V? It doesn't need a +/-9V supply. It's just the minimum voltage required to get +/-5V out from most op-amps.

author: uncle_bob
author_rank: Unknown
timestamp: February 27, 2016, 10:48:10 pm
content: Quote from: KermitDK on February 27, 2016, 06:03:35 pmHiGenerate the -5V with three 1K resistors in series. That way there is no need to find crazy value parts. Any error it adds to the gain is less than the tolerance on the two 1M resistors ....Bob

author: jwm_
author_rank: Frequent Contributor
timestamp: February 27, 2016, 11:12:42 pm
content: Quote from: uncle_bob on February 27, 2016, 10:48:10 pmI don't think the +/- 15V rails are regulated but are straight off the center tapped transformer full rectified. I could be mixing up my synthesizers though, I know some have 24V unregulated rails instead...

author: uncle_bob
author_rank: Unknown
timestamp: February 27, 2016, 11:17:41 pm
content: Quote from: jwm_ on February 27, 2016, 11:12:42 pmHiThe op-amp dies at +/- 16V. If the rails are un-regulated then you need to do something. 79L12 and 78L12 are a pretty easy pair to find and they will run ok off of a "sort of +/-15V" supply.Bob