Isolated PWM output

Facing the challenge of making an isolated DAC output I found a circuit by Kerry Wong (http://www.kerrywong.com/2013/10/01/an-isolated-dac-using-pwm-output/). Unfortunately, it did not work as I hoped. The optocoupler I used, a PC817 turned out to be too slow. It took some 20 us for the transistor to get out of saturation. Continue Reading

SIM900(A)

Did you struggle with a SIM900A module from ebay? Well, I did. I bought several from different vendors and spent some time to get them ‘online’ (or rather ‘on the air’). For a data logging project I bought 2 SIM900A modules. After I received them I found out that I Continue Reading