Variable pulse train generation

Question

I need to generate a pulse train with 12 bit resolution, controlled by an MCU.

The duty cycle can be in the range of 30 - 40%, while the frequency (0.5 - 32 kHz) is what needs controlling with 12-bit resolution.

The pulse train is to be used to control a Yaskawa Inverter which appears to operate under these parameters.

I think I have several options:

1. Find a chip that will generate this for me (controlled via SPI, I2C, etc).

2. Use a pulse generator like the 555, and find someway to vary the frequency using an output from the MCU - perhaps using the output from a DAC.

What is best way to do this?

Answer 1

Figure 1. The inverter provides several external speed control options.

You are not constrained to 32 kHz. Page 112 shows that the max pulse frequency can be set parameter H6-02 at anywhere between 1 kHz to 32 kHz (and as low as 100 Hz on some models). Setting a lower frequency may simplify the microcontroller requirements.

Your other option is to PWM the A1 or A2 input with a 5 V signal via an RC low-pass filter but set the parameter for the input scaling to twice the maximum speed you want. (This is because your 5 V micro can only give 5 V at 100% PWM into the 0 to 10 V input.)

Any micro with a PWM controller with ≥ 12 bits should be able to do this for you - including d'Arduino.

Note also that there's a Modbus interface so you can probably set and read the speed (and a load of other parameters) on serial comms thereby avoiding any analog circuitry.