I try to drive two small pcb coils. The coils have a resistance of around 14 Ohms (i dont know the L value). I have a PIC10F200 controlling the base of a BCV27. However i dont seem to get much more than 0.1V across the coils. Did i make a mistake, or is there something fundamentally wrong with my approach?

Thanks!! enter image description here

  • \$\begingroup\$ Probably something fundamentally wrong but, you haven’t stated what your aim is. \$\endgroup\$
    – Andy aka
    Aug 24 '20 at 18:37
  • \$\begingroup\$ What is your VDD voltage, and does it stay steady when you turn Q1 on? Your diode should be from the collector to VDD to prevent inductive kick, BTW -- you may have killed your transistor on the first try and now you're just seeing that. \$\endgroup\$
    – TimWescott
    Aug 24 '20 at 18:38
  • \$\begingroup\$ Report every node until Ohm’s law and the datasheet conflict \$\endgroup\$ Aug 24 '20 at 18:57
  • \$\begingroup\$ If the transistor is operational, similar values ​​should be measured at each point. The base current is unnecessarily high. R1 could be of much greater value. \$\endgroup\$
    – csabahu
    Aug 24 '20 at 19:03
  • \$\begingroup\$ 1&3 backwards on U1? \$\endgroup\$ Aug 25 '20 at 0:06

A fundamental error involves D1. Its anode should go to Q1's collector, not to GND.

A capacitor should be added from +5V DC supply to GND. This is not a fundamental error. But it will keep transient voltages from destroying your processor, and act as a local charge reservoir that will give your solenoid more "punch": something in the hundred(s) of microfarads.
When a solenoid is switched off, its stored energy dumps via D1 into the DC supply. The capacitor absorbs this energy and keeps the DC supply from momentarily rising...even a short transient above that which the processor can stand will cause destruction.

This processor seems to have 4 GPIO pins, one of which you are using to activate the solenoid. The other three pins are left open-circuit: their default state is to be GPIO input pins. Leaving high-resistance input pins floating is not good practice. Either change them to be outputs, or tie them to known logic states (high or low).


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