Electronics

scotthr · Joined: 02 Dec 2006 Posts: 6

Hello, we being the rednecks we are put a couple of 9mm rounds through the wall and into the hvac controller for our building. We found a replacement, however it is designed with analog inputs for 0-10 vdc.
All of the sensors are configured at 0-5 vdc.

Anybody have any ideas on what parts I need and maybe a schematic of how to make this work without having to spend the $$$ for the converters the company is trying to sell me.

I understand that an op amp will do this, however I don't know which one and what resistors I need to accomplish this goal.

Anyhelp with what parts and a schematic would be very helpful.

My other option is to lose accuracy by 50%

Thanks all Smile

neon · Joined: 25 Feb 2006 Posts: 580

You nees a gain of A=2 use lm324 or similar op-amps There are 4 amps in one package. the gain is a ratio of resistors 5k in 10k feedback from output . THE SCHEMATIC AND INFO YOU CAN FIND at datasheetlocator .com National semi. there are also applications notes for you to read if stuck good luck.Watch polarity since it is a differential amp.

scotthr · Joined: 02 Dec 2006 Posts: 6

Thank you for your reply. I have been doing alot of reading and now I need to know if I got this right.

vdc in --> R1 --> V+
V- --> ground
VCC + --> 12VDC Regulated
VCC - --> ground
V+ --> R0 --> vdc out

If I get this right then the input voltage will be amplified by the gain as set by the values of the resistors R1 and R0. Assuming the input voltage is +5vdc and the gain A=2 would produce +10vdc as the output voltage.

Is this correct?

If not where did I go wrong?

If so, what resistors should I get? I tried like hell to understand that part but got more and more confused. Can somebody tell me what kind of resistors to get?

neon · Joined: 25 Feb 2006 Posts: 580

i don't have spice to analyze something this simple.draw a schematic and attach then i will know. the R VALUE should be 10k in to - and 20k f/b to -[ tie 6.6k+ to gnd. A=2 INVERTED USE RL07 type or better for temp stability and the acuracy will be +/- 2% want better use R as +/- 1% or better plain carbon is +/- 5% pluss temperature drift

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