Trap Santa with the Raspberry Pi B+

RE: Trap Santa with the Raspberry Pi B+

D_Hersey — Thu, 06 Nov 2014 17:35:07 GMT

shabaz has a good point: Driving a 3.3V logic input with a five-volt signal is survivable but undesirable. Some of the cheaper solutions would be to shunt the input with a backwards 3.3V Zener would cost about 20c., inverting the signal and feeding it into a VN2222 low-Vgs mosfet would run about 50c.

BTW, love the concept and the project!!

RE: Trap Santa with the Raspberry Pi B+

shabaz — Thu, 06 Nov 2014 17:11:58 GMT

Hi Les,

Also, although there is a current-limiting resistor for the sonar device in the circuit, usual cost-sensitive practise is probably to use a potential divider (i.e. another resistor) to get the 5V logic output to work with the RPI, if the output changes slowly (normal practice would be to use a level converter).

RE: Trap Santa with the Raspberry Pi B+

D_Hersey — Thu, 06 Nov 2014 16:56:16 GMT

Shunting LEDs is a new one on me, didn't think they matched that well. Going without ballast resistors uses the on-resistance of the output transistors to limit current. Survivable, but rather dodgy. LEDs have a negative tempco of drop potential.