Circuit Summary
I've been watching this for a while, and I've (hopefully) sorted the speculation from the facts –
1] The bell housing sensor is a Variable Reluctance (changing magnetism) pick up. It generates a small amount of electricity whenever a piece of steel moves past. The electricity is alternating current, flowing in one direction as the metal approaches and the opposite direction as the piece moves away. Either end of the generating coil wires may be connected to ground and the other end will provide an oscillating voltage.
2] Toyota diesel flywheels have 108 teeth. So they produce 54 times as many pulses as a four cylinder petrol engine or 36 times as many as a 6 cylinder.
3] Petrol and Diesel tachometers have the same drive circuitry - an NEC C1006C motor driver chip supplies the power to swing the needle.
4] Petrol tachometers have some simple protection in front of this chip, and that's all.
5] Diesel tachometers have 2 additions –
A] an M51204 voltage comparitor is used to read the alternating current output of the flywheel sensor to produce Direct Current pulses and
B] a cmos 4024 ripple counter performs multiple divisions of the pulse rate.
6] For a 2H (6 cylinder) the division selected is /32. This is not quite /36, so I’m assuming the gain of the C1006C meter driver is adjusted down a little. I haven’t seen the circuit of a 2B tacho but I expect it to use /64 with the gain adjusted a little bit up.
So, to run a Toyota diesel tach from a petrol engine you need to condition the input and feed it directly to the big green capacitor (marked 223) that operates the meter driver. The resistor values around the driver may also need adjusting.
To run a Toyota petrol tach from a Toyota diesel pickup you need to reproduce the comparator and frequency divider stages. The resistor values around the driver may also need adjusting.
To run a generic petrol tach from a Toyota diesel pickup you need to reproduce the comparator and frequency divider stages. The divider can be made exact by using AND gates to make the count 32+4=36 or 32+16+4+2=54.
Is there an electronics whiz out there who can provide the circuit schematics for this?
I’m thinking bell housing pickup|comparator|counter/36|and_gates-->petrol tach.
Anyway I’ve got what I need to build a simple shift indicator for a diesel; I can take a clean cmos level signal from the ripple counter; either the clock input or the /32 output will do nicely.
bye
I've been watching this for a while, and I've (hopefully) sorted the speculation from the facts –
1] The bell housing sensor is a Variable Reluctance (changing magnetism) pick up. It generates a small amount of electricity whenever a piece of steel moves past. The electricity is alternating current, flowing in one direction as the metal approaches and the opposite direction as the piece moves away. Either end of the generating coil wires may be connected to ground and the other end will provide an oscillating voltage.
2] Toyota diesel flywheels have 108 teeth. So they produce 54 times as many pulses as a four cylinder petrol engine or 36 times as many as a 6 cylinder.
3] Petrol and Diesel tachometers have the same drive circuitry - an NEC C1006C motor driver chip supplies the power to swing the needle.
4] Petrol tachometers have some simple protection in front of this chip, and that's all.
5] Diesel tachometers have 2 additions –
A] an M51204 voltage comparitor is used to read the alternating current output of the flywheel sensor to produce Direct Current pulses and
B] a cmos 4024 ripple counter performs multiple divisions of the pulse rate.
6] For a 2H (6 cylinder) the division selected is /32. This is not quite /36, so I’m assuming the gain of the C1006C meter driver is adjusted down a little. I haven’t seen the circuit of a 2B tacho but I expect it to use /64 with the gain adjusted a little bit up.
So, to run a Toyota diesel tach from a petrol engine you need to condition the input and feed it directly to the big green capacitor (marked 223) that operates the meter driver. The resistor values around the driver may also need adjusting.
To run a Toyota petrol tach from a Toyota diesel pickup you need to reproduce the comparator and frequency divider stages. The resistor values around the driver may also need adjusting.
To run a generic petrol tach from a Toyota diesel pickup you need to reproduce the comparator and frequency divider stages. The divider can be made exact by using AND gates to make the count 32+4=36 or 32+16+4+2=54.
Is there an electronics whiz out there who can provide the circuit schematics for this?
I’m thinking bell housing pickup|comparator|counter/36|and_gates-->petrol tach.
Anyway I’ve got what I need to build a simple shift indicator for a diesel; I can take a clean cmos level signal from the ripple counter; either the clock input or the /32 output will do nicely.
bye
Last edited:
