ESP8266 Community Forum

- Thu Dec 10, 2015 11:56 am #36171 Hi Guys,

This is one of my first projects, so am still learning .

Ok, so I've got a 3V doorbell (Friedland D902), which apparently should take 200mA (they are not very clear on this though). When I power my NodeMCU (it's the LoLin "v3"-version with a 1777 voltage regulator) of a USB 2.0-port and connect the bell to the 3V and GND on the ESP, success! -- a nice ring --

However.. when I add a pull-up resistor and low-pass filter to the D1 (to take not of the doorbell button), there seems to be no enough juice left for the bell. The result is a moving bell hammer, but not hard enough to make it ring.

The D1 gets input from the doorbell-button from about a meter of two of wire (hence the filter).
Like this: DOORBELL BUTTON (long wire) - 100ohm -then from there splits -> 100K pull up to +3.3V and -> 0.1 uF to NEG, and the wire finishes on D1 (hope that's a clear enough description).

So on this set-up (that works quite well filtering out radiation false positives), the 3.3V doesn't seem to provide enough amps to power the bell anymore (eventually I'd run this through a relay, but even connecting straight to the bell now isn't powerfull enough anymore)... Isn't that odd? - Thought that a pull-up wouldn't take a whole lot of power..

Any suggestions anyone?

- Thu Dec 10, 2015 1:36 pm #36174 a 100K pullup resistor consume almost nothing. So, there problem is probably elsewhere.
Maybe you should draw your schematic and post it, things will be clearer.

- Thu Dec 10, 2015 6:13 pm #36189 @Stu

If I got it right, D1 has the three components attached.

1) What is the voltage arriving from the DOORBELL BUTTON when it is open/closed?
2) What is the voltage at D1 when the button is open/closed?

Anyway, the voltage drop across the 100R should tell you how much current is drawn from the wire.

- Thu Dec 10, 2015 6:55 pm #36193

Any suggestions anyone?

The 100 ohm resistor, maybe, is too limiting. Measurements required.

But... some things simply shouldn't be done. Like, don't use the NodeMCU's onboard 3.3v regulator to drive a dirty great load like the doorbell. The onboard regulator is for the ESP8266 and maybe some glue logic... period.

(Please don't tell us you have been driving the bell directly from one of the GPIOs ... this could kill the ESP8266 )

3.3 v regs are like 10 cents each, so you can add a separate one for the doorbell. Or even 3 1N4001 diodes ( 3 x 0.6v drop = 1.8v drop) in series from a 5v supply. Use a suitable MOSFET to control the doorbell with a GPIO.