We have a new problem: when the load is connected, the voltage drops so much that the lower threshold for turning the relay off is reached and the load is disconnected. That in turn causes the voltage to rise again and the load is immediately turned on again, etc.
Here is the oscillation:
one pulse:
what happens if we only connect the BPro to the power supply which is set to 4.8 Volts:
and a simple 4.7 Ohm 10 Watt resistor at 4.8 Volts:
Fortunately, the LM3914 has 9 outputs and therefore 9 voltages to choose from for the hysteresis. When I moved the hysteresis points further apart, it worked. I suspect that with the voltage drop , the two threshold voltages may have overlapped.
In the meantime, the USB boost converter has burnt out, so I am using a bigger model made by SainSmart. Here is the new board:
Replacing the Relay with a MOSFET
We can also use a MOSFET (typically n-channel) as a switch.
We want to use a MOSFET that has low resistance at 5Volts. The IRL (L for logic) series is designed for that. In the specification, look under the RDS row for the voltage which should be 5 Volts.
https://arduinodiy.wordpress.com/2012/05/02/using-mosfets-with-ttl-levels/
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