XY-PWM signal generator

Introduction

This device can be used if we need to generate PWM signals. It has hardware buttons, so we can adjust frequency "by hand". It also has RX/TX pins, which allows us to change the frequency programmatically, say, from Arduino.

Powering it up

A rather cheap solution (a jumper would be much more convenient) is a "cut this wire if you want to use an external power source (rather than USB power). I am going to use an external power source, so I took a knife and cut the wire.

A VERY important note: if you use NodeMCU as a controller, it can not provide 5V power for generator, so you need a separate power source. One can think that it is possible to do with Arduino's provided 5V: the answer is NO. As you connect Arduino's 5V as a power source, the generator drains too much power and attemp to upload a sketch fails with something like:

avrdude: stk500_getsync() attempt 1 of 10: not in sync: resp=0x00

At the photo below, ypu can see Arduino powered by USB from the PC, while the generator is powered through a separate 5V power sourcs: this approach works fine.

Setting it up

The following is a surprisingly detailed description I have copied from Ali (usually they have no descriptions whatsoever):

Two independent generators, you can set frequency and working cycle.

...

Frequency is represented as three ranges:

Example:
"100" means that the frequency is 100 Hz;
"54,1" means 54,1 kHz;
"1.2.4" means 124 kHz;

Working cycle is in range 0 - 100;

All three frequences of the working cycle are the same, all parameters are not energy dependent.

Module parameters:
Working voltage is 5 - 30V, micro USB power is supposed to be 5V;
Frequency range 1 Hz - 150 kHz;
Frequency is within ± 2%;
Output current: <30mA;
Output voltage: 5V (can be set);
Temperature range: -30 ~ +70°;

Setup:
The module has 3 setup buttons: set, up, down;
Press [Set] to select one of four parameters: (FR1: frequency PWM1; dU1: working cycle PWM1; FR2: frequency PWM2; dU2: working cycle PWM2), before parameters are set, the corresponding name will flash.
Set [Up], [Dn], to change the parameter value (long press is supported).
Two independent outputs, each can be set separately, (XXX: 1 Hz ~ 999 Hz; X X.X: 0,1 Hz ~ 99,9 Hz; X.X.X .: 1 kHz ~ 150 kHz);

Serial control
Data transfer speed at 9600 bits per second;
Data bits: 8
Stop bits: 1
Parity: no
Flow control: no

1. Setting frequency
«S1FXXXT»: setting PWM1 XXX Hz (001 ~ 999)
«S1FXX.XT»: PWM1 X X.X kHz (00,1 ~ 99,9)
«S1F: X.X.X.T»: PWM1 XXX kHz (001 ~ 150 ..)

'S1': PWM1
'S2': PWM2
'F': frequency
'D': working cycle
'T'-flag of the end of command

Setting the working cycle
«S1DXXXT»: setting the working cycle PWM1 XXX; (001 ~ 100)
"S2DXXXT": PWM2 working cycle XXX; (001 ~ 100)

Connecting it to Arduino

In this particular project I used Arduino Uno, it only has one pair of serial pins: 0(RX) and 1(TX). The following program sets frequency from 50 Hz to 900 Hz, and then to 50 Hz again, in cycle. It also can optionally blink a diode, which is just a decoration.

Note that I am not sending any logs to PC by Serial: serial is used to control the generator.