The LM2907 series of tachometer circuits is designed for
minimum external part count applications and maximum versatility.
In order to fully exploit its features and advantages
let’s examine its theory of operation. The first stage of operation
is a differential amplifier driving a positive feedback
flip-flop circuit. The input threshold voltage is the amount of
differential input voltage at which the output of this stage
changes state.
Two options (LM2907-8, LM2917-8) have
one input internally grounded so that an input signal must
swing above and below ground and exceed the input thresholds
to produce an output. This is offered specifically for
magnetic variable reluctance pickups which typically provide
a single-ended ac output
The differential input options (LM2907, LM2917) give the
user the option of setting his own input switching level and
still have the hysteresis around that level for excellent noise
rejection in any application. Of course in order to allow the
inputs to attain common-mode voltages above ground, input
protection is removed and neither input should be taken
outside the limits of the supply voltage being used. It is very
important that an input not go below ground without some
resistance in its lead to limit the current that will then flow in
the epi-substrate diode.
Would be with one teeth, but 2450 with the 12 teeth gear wheel you showed!anyway 490Hz it’s like 29400 rpm
Another one: if it’s possible to change the position of the sensor and to adapt the spokes to trigger so you’ll have less pulses per minute.
I still think, that a photointerrupter would be the most easy solution
Basically yes, but the optical beam should be in parallel to motor axis. Don't know about the thickness of your gear wheel? IR-LED/phototransistor could be used with a few cm distance at maximum without optics, also a tube to shield enviromental light may be necessary at the phototransistor. You can also use visible red LED, but IR would giver higher response. Notice that LED and phototransistors are available with different optical half angles. Low half angle should be preferred.The ON will be represented when a beam can pass between the gear wheel.The OFF would be represented when a beam cannot pass between the gear wheel(because a tooth would be blocking the beam).
The picture attached it's only to understand the position of the sensor.FvM said:...Would be with one teeth, but 2450 with the 12 teeth gear wheel you showed!anyway 490Hz it’s like 29400 rpm
I see.The picture attached it's only to understand the position of the sensor.
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