Relay buzzer

As a test of mostly breadboading, I breadboarded this 12V relay buzzer from a couple of random NPN transistors and a microwave oven relay:

$ 1 0.000005 0.010109782498721881 50 5 43
R -48 64 -48 32 0 0 40 12 0 0 0.5
r -48 64 -48 176 0 1000
t -48 176 32 176 0 1 0.6207115498642259 0.6788785101220731 410
t -96 192 -48 192 0 1 -0.02761021024479937 0.6512682998772737 760
r -96 192 -176 192 0 1000
g -48 208 -48 256 0
g 32 192 32 256 0
178 80 128 80 80 0 1 0.2 0.019618688531384095 0.05 1000000 0.02 280
w -48 64 0 64 0
w 64 64 64 80 0
w 64 64 144 64 0
w 144 64 144 176 0
w 32 128 32 160 0
w 48 128 48 176 0
w 48 176 144 176 0
w 80 128 256 128 0
w 256 128 256 368 0
w 256 368 -176 368 0
w -176 192 -176 368 0
d 0 128 0 64 2 default
w 0 128 32 128 0
w 0 64 64 64 0
x -56 319 146 322 4 12 Relay\sbuzzer\swithout\sNC\scontacts

Falstad’s simulation runs the relay at 200kHz by default, much faster than the relay I have, which is at about 100 Hz.

It was frustrating and slow to build the circuit because:

• I was making jumper wires by sanding varnish off coarse magnet wire with sandpaper between my fingers;
• I didn’t know the pinouts of the transistors or the values of the resistors (actually I think one of them may have been 1k5Ω)
• probing the breadboard with probes that don’t fit was pretty inconvenient;
• I broke a leg off Q2 during the process, and that took me a while to figure out;
• a multimeter with no audio is a slow way to check out the circuit.

However, once I had it all connected and checked out with the multimeter, I plugged it in and it ran. This was satisfying.