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Output voltage ramp up and down for input voltage window
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harnon:
Sorry for the horrible topic title, but I've got a slightly random fun project idea where I want an output that become active if the input is within a given voltage window. In other words, if the input voltage is less than V1, or greater than V2, then the output should be 0V. In between these values the voltage should increase to Vdd up to the midpoint then decrease afterwards. As its a fun project, I'd like to do this without a microcontroller.



The idea eventually would be to chain a bunch of these together so that, i.e. it could for instance control a wave of LEDs fading in and out as the input voltage sweeps. I suppose something similar to the battery level indicator video Dave did but with the voltage ramps and probably quite 2-5A currents :D

I can do the left hand half of the ramp using a single supply opamp and a voltage divider the reference voltage, however I'm not sure how to cut over to a downward ramp the voltage back down to 0 output above Vmid.

Is this even possible without a uC? I'd like to try and solve this by myself for The Learning, any hints or things to learn about to get me started?
Ian.M:
You'll need a whole mess of OPAMPs configured as differential amplifiers for level shifting, a precision full-wave rectifier (but diodes reversed for negative output) to get your triangular ramp up then down, and a precision half wave rectifier to cut off the skirts of the triangle where they cross 0V.  Better bulk buy the matched resistors you'll need, A pack of 100K 0.1% should do nicely.  Keywords for Google in bold, search: OPAMP <keyword_string>

LTspice solution attached.  Download it *AFTER* you've figured it out for yourself!

@All: If you want to comment on or improve my solution, out of respect for the O.P's desire to figure it out for them self, please be careful what you say in your post.  Full, un-censored comments can be attached instead.

Edit: Sim needs a load resistor - see below  :palm:
harnon:
Thanks Ian, sounds like a lot of googling and pondering on the cards for me :)
Ian.M:
N.B.  The problem is complex enough with split supplies.  I wouldn't recommend attempting a single supply version until you fully understand all the OPAMP circuits I suggested Googling, and have built and tested a split supply version.

Also, if you want to fade LEDs you'll need an OPAMP V=>I converter stage on the output.
lordvader88:
As for timing when to cross the peak of the triangle, I'm sure some way could use derivatives. But what about timing how long it takes to get 1/2 way, then have some transistor turn on/off and shut down a positive ramp. And at the same time a decreasing ramp gets turned on. Maybe some peak detector triggers a 555 that flips 1 ramp off and 1 ramp on.

IDK, I should play around more.


A lot of electronics is an awful lot like mechanics and machines. No wonder we love electronics too
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