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Adjustment of
Car speed detection device

The door lock signal is adjusted before installing to the car. Power supply(+12V) is connected and the line that connects door lock control solenoid connects and also cut to the ground wire.
When the wire is separated from ground, the RL3 and RL4 operate simultaneously and adjust the VR2 as the RL4 releases after about one second.

You install and carry out this adjustment to the car.
VR1 is adjusted as the relay RL1 operates at the speed of the car is 10 km/h.
It does not need to set up rigidly.
In the case that the speed of the car is low, the even circuit does not work sufficiently, then the relay chatters a few. You do not need to worry about it.

You carry out it like the adjustment of door lock speed.
VR3 is adjusted as the relay RL5 operates at the speed of the car is 40 Km/h.
Alos it does not need to set up rigidly.

The frequency of the car speed pulse signal differs by the kind of the car.
There are 2 pulse method and 4 pulse method fundamentally.
You do not understand usually which method the car of yourself is.
Even I do not know which method the car of myself .
It was about 30Hz with the 40km/h when it measures with the frequency counter.
Therefore, I make it a rule to carry out the setting of speed detection with VR1 or VR3.
Yet, when the number of the pulse differs 2 times as shown above, It might not made with the value that the setting of speed detection is introducing with the circuit drawing.

Calculation of R15

R15 is such a thing that decides the setting range of the detection voltage by VR1 in the detection circuit of the speed 10 km/H.
The voltage setting range in VR1 becomes 0V to 6V in the case of R15 is 0 ohm (short circuit).
The voltage that sets up with VR1 is around about 0.7V, but setting voltage changes largely just a few of VR1 moved and adjustment is difficult.
Thereupon, making the range of narrow where can change with VR1 by inserting R15 and setting is done easily.

For example the voltage range to make 0V to 1.2V in VR1 is calculated as follows.
The current when the voltage of VR1 is 1.2^V : 1.2^V / 1^Kohm = 1.2 mA
The voltage that adds to R15 : 6^V - 1.2^V = 4.8V
The resistance value of R15 : 4.8^V / 1.2^mA = 4Kohm

3.3K ohm is being used for R15 in the circuit drawing.
In this case, the voltage that adds to VR1 is 6^V / (3.3^Kohm + 1^Kohm) = 1.4V.
then the setting range in VR1 becomes 0V to 1.4V.
Also, the voltage of D6 differs by the part.
It is the one that produced it actually and was 5.4V.
Therefore it is the one that produced it and the VR1 voltage setting range is 0V to 1.26V.

Calculation of R26 and also R27

R26 and R27 are such a thing that decides the setting range of the detection voltage by VR3 in the detection circuit of the speed 40 km/H.
Such calculation that makes the setting range by VR3 1.2V to 2V is shown below.
First of all, R27 is calculated.
The current when the voltage of VR3 is 0.8V(2^V - 1.2^V) : 0.8^V / 1^Kohm = 0.8mA
The resistance value of R27 : 1.2^V / 0.8^mA = 1.5Kohm
The voltage that adds to R26 : 6^V - 2^V = 4V
The resistance value of R26 : 4^V / 0.8^mA = 5Kohm

In case of R26 is 4.7Kohm, R27 is 1.5Kohm, the voltage setting range is as follows.
The current that flows to R26,VR3 and R27 : 6^V / ( 4.7^Kohm + 1^Kohm + 1.5^Kohm ) = 0.83mA
The voltage that adds to R27 : 1.5^Kohm x 0.83^mA = 1.25V
The voltage that adds to R27 and VR3 : ( 1.5^Kohm + 1^Kohm ) x 0.83^mA = 2.1V
Therefore the voltage setting range in VR3 becomes 1.25V to 2.1V.

In the case that the voltage of D6 is 5.4V, the setting range of VR3 becomes 1.13V to 1.88V rate.

Change of the car speed and detection voltage in the production work

The voltage change of No.4 pin of IC1(2/2) by the frequency of the car speed pulse signal is shown below.