Frequency to voltage converter circuits for RPM sensing, options? - Page 1
Forum section: electronics / beginners

author: G-son
author_rank: Regular Contributor
timestamp: April 06, 2023, 05:56:09 pm
content: I'd like to have frequency to voltage converters for uses such as tachometers and rpm feedback to a speed regulator.I know of the dedicated LM2907 and LM2917 circuits, but I'd like to know what other options there is using more common components. I have seen something using a 555 timer, not sure where I saw it but it might be worth a try. Do you have any other suggestions?

author: max_torque
author_rank: Super Contributor
timestamp: April 06, 2023, 07:35:09 pm
content: These days i just use a small micro. Today a little arm mico is cheaper than the components you would use to do this conversion in the analogue domain and it offers infinite customasation options for input to output scaling etc.Ok, i guess it depends if you want to stay analogue, but given that increasingly instruments have data links (CAN , LIN, etc) here the micro also gives you options.You still need a suitable front end to turn what is probably a varriable amplitude signal into a square wave (depending on the exact type of sensor used) of course

author: Benta
author_rank: Super Contributor
timestamp: April 06, 2023, 08:01:34 pm
content: I'd just go with the LM2907, it doesn't get any simpler/cheaper. No need to reinvent the wheel.

author: mikerj
author_rank: Super Contributor
timestamp: April 06, 2023, 09:33:51 pm
content: You could use a 555 configured as a one shot (monostable) followed by an integrator.

author: Picuino
author_rank: Super Contributor
timestamp: April 06, 2023, 10:02:26 pm
content: The frequency of an encoder can be measured very accurately and quickly in a microcontroller controlling the rotational speed of a motor. Moreover, the pulses can be counted to accurately measure the position of the motor as well.Why would you want to lose position information and speed accuracy?

author: BeBuLamar
author_rank: Super Contributor
timestamp: April 06, 2023, 10:47:05 pm
content: I use a WAGO 857-500 Frequency to Voltage or Current Converter. It's not a cheap solution but an easy solution.

author: G-son
author_rank: Regular Contributor
timestamp: April 06, 2023, 11:21:19 pm
content: I am hesitant to using microcontrollers because, basically, I don't understand them and I'm not really interested in understanding them. The closest I've been to programming was some basic use of PLC in school 25 years ago, I didn't have the patience for it then and even less so today. It just isn't fun for me, and if it isn't fun...I know microcontrollers can do many jobs very well, they're probably the best choice lots of times... but it's not for me.I like analog circuits much more. 555 and integrators make sense to me, some time studying a datasheet and schematics is usually enough to figure out how a circuit works and what to change to make it work differently - which can be fun with something like the 555 as it was meant to do a couple of different jobs as a timer but people have used it for countless other purposes doing just about anything. I've never used the LM2907, but that also makes sense just by reading the datasheet, and I do think I already have one I bought years ago.I will take a closer look at that, I just wanted to ask about alternatives because there are usually a bunch of ways to solve a problem, might as well try to fins many options before picking one to run with.

author: geggi1
author_rank: Frequent Contributor
timestamp: April 07, 2023, 11:42:24 am
content: I believe you can use a RC circuit to do this.You will have to do a bit of testing and calculation but it should be possible.By setting the circuit up with a resistor for the input signal and a resistor in parallel with the capacitor you will have two RC circuits.What you are using to measure must be high resistivity compared to the resistors in the RC circuits. A simple solution is to use a op-amp as a buffer before your instrumentation because this will give you control of the input resistance of the instrumentation.

author: David Hess
author_rank: Super Contributor
timestamp: April 07, 2023, 04:24:30 pm
content: Analog tachometer circuits use a charge pump to convert the pulse repetition rate to a voltage or current.