Measuring speed and distance

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On this page you will find informations to measure speed and distance of a vehicle, with an APF27.

Principle

On one wheel of your vehicle, you will have a system with some holes that will generates a square signal. Each pulse will correspond to one or more turn, depending on the precision you need. == a kid of tachymeter. You have to adapt the signal level to 0-2,8V and limit the overshots.
Then, you will be able to inject on the TIN input of the APF27. This is only possible if you have an APF27Dev without HDMI chip. The TIN input is internally linked in the i.MX27 to some counters that we will configure and use to count the signal pulses.

Montage

Montage _WITH_ AD9889 on APF27Dev

TIN on APF27Dev (left side of R24 resistor)

Test

• Load driver that will allocate GPT2 timer:

# insmod gpt2_plat.ko

• Configure GPT2 for taking TIN as input and activates it:

# imxregs TCTL2 0x00000007

• Check that counter is increasing:

# imxregs TCN2

GPT Counter Register 2
TCN2                     0x00000022  -> 00000000 00000000 00000000 00100010