I realise that close to zero hertz the output may become erroneous but I'm primarily interested in the upper end of the scale and tracking the speed between 250 and 500 hertz. The circuit will be used for input signals ranging from zero to around 500 Hz maximum (maybe I need a frequency multiplier in this design?) Hopefully the output signal will be an analogue voltage that more or less follows the input frequency. I haven't had the time to breadboard this circuit yet the input section works OK and is the design I'm currently using in the prototype instrument the section with the 4046 has been adapted from a Forrest Mims book (where else). However, taking up your suggestion of the 4046 and pin 10 as the output here's a circuit diagram using the IC to convert the frequency signal to an analogue output voltage. Sorry to inform you DickCappels but there's no computer in this project it's all soldered onto a PCB and mounted inside the instrument. This is single chip solution, your 555 may act as the monostable in which case throw away the 2917 and feed the 555 O/P in to the filter I've described.(3 components, use a 1n4148 diode) Hope thats what you were wanting from the circuit, schematic avail on request.Ī micro will do it, but you'll have to learn programming etc. The LP filter time constant needs to be 'relatively large' at say 10-20ms if that is an acceptable delay so use 220nF and 10k. The output can then be fed to the two '14 gates you have at your O/P. But put a diode across the resistor so the capacitor will discharge instantainously on a negative spike. Feed this output into a resitor and cap to ground (Normal LP filter). Set the period of the monostabe to (say, as its adjustabe) 2.5ms = 400Hz Then the o/p will be contiuously Hi above this speed or will have low going spikes below this speed. Do this using a monostable which can be made adjustable. If I'm right in thinking that when the wheel passes a certain speed (Not acceleration) you wish a digital output to be activated.
Also, if the instrument gets bumped during use you could well get an extra beat in the rhythm! A tacho-generator would be another alternative, but from what I've seen these devices are not that compact and rather expensive for the experimenter. I was thinking of using accelerometers but then there's gravity to consider and the problem of mounting the sensors on the wheel and having to use slip rings or radio to transmit the output signals. What I'm looking for is some kind of circuit that give a fast response to the acceleration of the wheel I don't really need an accurate measurement but a rapid response is my main concern. Every time the crank is accelerated (above a set speed) the signal from the 2917 triggers an analogue switch to control the sound effect for the rhythm.
The circuit is used in the yellow instrument in my avatar photo. The output from the 2917 is the overspeed indicator and triggers when the wheel runs above a certain speed this limit is adjusted by the trim pot (tirant) in the diagram. This signal is then fed through a 555 timerġ) to create a good clean signal for the 2917 andĢ) to guarantee no signal when the wheel comes to rest. I've attached the schematic to this post.īasically the IR diode/sensor generates pulses from holes in the rotating wheel. I've never used a microcontroller before but it sounds like the ideal solution. I can't accept the 1 second time delay but can jimkeith (or someone else) please explain a little more about the alternative approach using the microcontroller.
Zero input delay pickaxe code#
"The low frequency is a problem-to reduce ripple in the analog output, a relatively long time constant is required-to obtain accurate readings with low ripple, a time period of 0.5sec to 1sec is required for the voltage to settle-is this time delay acceptable?Īnother way to do this is via a microcontroller that measures time between pulses calculates 1/t and outputs an analog signal-relatively simple problem for a high level language code developer-this provides fast response without ripple-probably beyond the scope of your problem-do you agree?" I noticed a quote from jimkeith in a recent post on a similar subject: The current design uses a 2917 chip for the F/V conversion, and this works OK at slow speeds but the delay is not acceptable at medium or faster rates. My project involves the conversion of a frequency of 500Hz (max) and I need a fast response time for this conversion.
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