Hi Sgt Wookie, appreciate this is a very old thread but believe it will solve my problem but have a question. Post 11 make perfect sense with the 4040 but am struggling to understand reply 12 and the 4017. My issue is I have a 60 tooth pickup on my prop shaft that is used as a speed sensor to drive speedo and electronic power steering. Have 2 cars with same setup but different diff ratios so believe I need to trigger a pulse on one car at 44 teeth and 50 on the other one. The input is using a hall effect sensor so that would be the clock so the circuits above would seem ideal. Looking at post 12 it looks like U2 is the units and U3 the 10's so my question is my would you cause U2 to reset when Q6 goes high. Should that not be U3. Am sure I am missing something so hope you see this and happy to reply regards RegMikeML,
Hope you don't mind; I decided I'd experiment with your circuit a bit. Your circuit has an advantage in that it would be much easier to convert for multiple gear teeth count selections using rotary switches or the like.
There are also fewer propagation delay issues to deal with than in my circuit.
I changed the 4011 NAND gate to the 4093 Schmitt-trigger quad NAND gate; the Schmitt-trigger allows simplification of the clock circuit along with making it impossible to "stall", and enables more reliable suppression of the "glitch" in the output due to the propagation delay issues both of our circuits have. It also enables dispensing with the 4049 inverters altogether.
As shown, the oscillator output has a range of about 418Hz to 6.3KHz, directly corresponding to an RPM range of 418 to 6,300.
So, one of the Schmitt-trigger NANDS is used for the clock, two as you had used the 4011's, and the last NAND is used to ensure the output is squared up from the filter. Since the output from the last NAND is inverted, it was necessary to use an NPN transistor to correct the output polarity of the signal.
However, this is likely very desirable; I suspect the sensor used in the vehicle is an open-collector output Hall-effect sensor. If that is indeed the case, resistor R5 would not be necessary, as the pull-up resistor would be inside the ECU.
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