Electronics > Beginners
How do I simulate an electric bell in QUCS?
cogburnd02:
I have an electric bell, which I would like to trigger from a couple of transistors (a smallish npn transistor switching on a larger pnp transistor switching the bell directly, with an arduino switching on the smaller first transistor. (I can post the part numbers of the transistors I was thinking about using if that'll help.))
How do I simulate this in QUCS? As a relay in series with an inductor and then in series with itself? If I am supposed to use the 'relay' part in QUCS for this, how do I measure/figure out the hysteresis voltage of the part I have? (I have a good multimeter, LCR meter, and scope.)
Here's some pictures I found on the web that look like the device I have: enclosed, (https://images-na.ssl-images-amazon.com/images/I/61Bu9utZmtL._AC_SL1500_.jpg) open (http://catalog.miniscience.com/catalog/electricity/Buzzer/Electric_Bell_Doorbell_m.jpg). And here's the wikipedia diagram (https://upload.wikimedia.org/wikipedia/commons/9/95/Electric_Bell_animation.gif) explaining the theory.
Zero999:
Just one question: why?
I woudn't bother, just model the bell as a resistor which draws the amount of current specified on the bell's datasheet or measure the resistance, with a multimeter, if that's not available.
Add a diode in reverse parallel with the bell, to protect the transistor from the inductive back-EMF generated when it's turned off.
cogburnd02:
I'm fairly sure that the bell introduces a 'ringing' in the line (https://en.wikipedia.org/wiki/Ringing_(signal)) (or perhaps just oscillation) and I just wanted to make sure that I wasn't--at any point--driving (too much current or voltage) either of the two transistors or the arduino output pin over/out of spec.
Zero999:
--- Quote from: cogburnd02 on October 17, 2019, 04:24:58 am ---I'm fairly sure that the bell introduces a 'ringing' in the line (https://en.wikipedia.org/wiki/Ringing_(signal)) (or perhaps just oscillation) and I just wanted to make sure that I wasn't--at any point--driving (too much current or voltage) either of the two transistors or the arduino output pin over/out of spec.
--- End quote ---
Have you had any problems with the circuit? Simulation can't tell you everything. There are plenty of circuits which will work in simulation, but not real life and vice versa.
To answer your question. There will be ringing, but not at the audio frequency produced by the bell. Look at how the bell works. When the bell is first turned on, the clapper will be away from the bell and the contacts in series with the electromagnet will be closed. The electromagnet is an inductor, with a certain internal resistance and capacitance, forming an RLC circuit. The inductance will probably dominate first, causing the current to initially be quite low, gradually rising, until the clapper hits the bell and the contacts open. An arc will form across the contacts and the RLC circuit will ring, probably at a frequency between a few 10s to 100s of kHz. The arc will also produce much higher frequencies, up to the microwave range and beyond, which can cause more trouble.
It's possible the spurious RF emissions could interfere with other the microcontroller, but it isn't something a simulator will be able to predict. To start with, just connect a reverse parallel diode in parallel with the bell, to suppress the high voltage produced, if the transistor interrupts the current, whilst the electromagnet in the bell is turned on. If you have problems with interference, they can be cleaned up with a snubber network (an RC circuit in parallel with the bell) and ferrite beads.
cogburnd02:
> Have you had any problems with the circuit?
I haven't built the circuit yet. I want to make sure I'm not going to zap my transistors and arduino before building the circuit.
> not at the audio frequency produced by the bell
Yeah I figured it would be at the same frequency that the bell goes clack-clack-clack-clack-clack-clack-clack at when I hold the ringing part of the bell, but it's powered on (& 'ringing')
Thanks for the other stuff.
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