Analog Tachometer

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pacificblue

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Hi, I'm new here.
I need to make an analog tachometer, with operational amps, and whitout integrated chips.
I see the integrated LM2917, but I can't use it.
How can I make an analog tachometer???
I Can use a sensor, operational amps, and digital display.
all circuit must be analogic, except the display.
(Input Analogic, Output Digital).
every idea will help me a lot.
Please Help Me!!!!!!
Thanks a lot.
Felix
 

All you need is a 555 in monostable mode, feeding an analogue meter - try googling for '555 tachometer' and you will find plenty of examples!.
 
pacificblue said:
Hi, I'm new here.
I need to make an analog tachometer, with operational amps, and whitout integrated chips.
Click to expand...

err an opamp is an integrated chip
 
Nigel Goodwin Thanks for your help, I hope to find a 555 tachometer.
Styx, yes, you are right, What I tried to say is that I can't use any intagred circuit except the operational amps, and a sensor.

Basically I have to make an analog tacho, using elemental analog components like op. amps., Transistors, diodes, LED, etc.

Please help me with this tacho.
Taks a lot.
Felix
 
This is doable but a bit more info is needed.
what do you have at present?

What I would do is get a brushed DC-machine and its output loaded with a 10k/100k/??k resistor and that signal fed into an opamp to filter and attenuate the signal. Then via calibration you can set 1V=1000rmp or 1V=100rpm whatever you want

IF you have a disc that spins and it sends out a pulse every revolution then an integrator cct will be needed to produce a very crude DC voltage

both ideas are analogue based (as oposed to digital which I gather you cant use )

as I said a bit more info of what you are intefacing to
 
A 555 is an IC also.
What are you measuring the RPM of? Is it a rotating shaft, or an internal combustion engine, or...?
 
More info

Styx Thanks for your help.
What I would do is get a brushed DC-machine and its output loaded with a 10k/100k/??k
Click to expand...
I don't understand whats is a brushed DC-machine.
Sorry if I don't undestand some things, because English is not my original Language.
The project has to be more siply as possible.
We can use to display results digital circuits, like BCD, display,etc, but now Mi Problem is whith the analog part, beginning measuring the signal, and finishing in the digital part, that I know how to do.

Ron H I need to measuring the RPM of a liltle motor, like a cassette or any toy.

Thanks all of you for your time and your help.
Felix
 
My problem is with the sensor. The type of sensor you use depends on the device (motor) you are trying to measure RPMs on. The motor needs to have some way to attach a sensor to it. Have you worked that part out?
 
Re: More info


Brushed DC-machine is a type of electric motor/generator.
INduction machine,syncronous machine,universal machine, variable reluctance machine are all different types.

The speed that the machine rotates (when operated as a motor) at is proportional to the voltage applied to it. Eqaully the voltage developed at the machines terminals (when operated as a generator)when it is rotated is proportional tothe speed the rotor spins at.

Thus brushed DC machines make good tacho's since all you have to do is use an OPAMP on the machine windings any you have a voltage proportional to the speed.


What ppl here are trying to get from you is what do you have at present

you must have some means of speed-sensing (hence my method of attaching another machine to the rotating body)

give us this info and it is solvable
 
Sensor

I think to use a sensor, with a LED and a PhotoTransistor.
and to measure the revs with the light pulses.
is that correct?
Is there some easier example??
I could measure RPMs of a motor what I want, because, The objective is only the correct work of the tacho.
My problem now is how to process this signal?.
Thanks.
Felix
 
ok so what you have produces a pulse ever rev? is that correct?

so all you need to do is "count" those pulses or count the freq of those pulses to get your RPm (well RPS then its just a factor of 60).

For some reason a PPL is comming to mind for this
 
Counting the pulses is not analog. You need to use the pulses to trigger a 555 one shot. Then, as the frequency increases, the dead time decreases and the filtered output DC will rise. The DC can be measured with a digital voltmeter to indicate speed.
 
Siliconchip did a 'rat it 'article a few months ago on an analog tacho based on the lm2917. By simply using a reed switch and magnet and changing a few resistors and old tacho board from a car was made into an analog rpm gauge for a drill press. Can't get it any easier than that article and I picked up an old tacho from the wreckers for the princely sum of $2.00.

Cheers Bryan
 
For Those Beginners here, here is a Simple Explaination:

The 100 ohm reaistor and Zener Stabalize the DC Voltage.
The 1 uF Cap allows the Pulses from the coil to pass through and get rectified by the two diodes.
The pot limits the DC signal going to the volt-meter. (comprized of the 270 ohm resistor and the meter.)

I Recommend a Minimum 1 Watt, 100 Ohm Resistor and a 5 watt Zener.

Been Using it for Years and it Works Very Well.

Enjoy.....Gary
 
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