I'm looking to build a little oscillator, generating (say) 100Hz, powered by a battery.
Looking at the wikipedia mutivibrator article, it talks about what the values for c1 and r1, and c2 and r3 should be. But what values are suitable for the two other resistors: r1 and r4? Should I pick an arbitrarily high value? A low one? One that's some multiple or fraction of the other two resistors?
Here is a good description you need.
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LarryD:
Here is a good description you need.
http://www.electronics-tutorials.ws/waveforms/astable.html
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Thanks. Found what I needed in a comment:
Resistors R1 and R4 act as collector load resistors so their value depends on the Ic current rating of the switching transistors used and the supply voltage, Vcc. Anything between 1k and 10k would do. If you use a lamp or led instead, use a resistor value to give the required current.
Next question - where do I take the output? Do I take it off the collector of the transistors?
Actually, having said that it's now starting to look like something I'm familiar with from fooling with arduinos: a switch with a pull-up resistor.
Outputs are taken at Q and Q'
These are at the collectors of the two transistors.
Edit
There is a table for R and C in the link I gave for setting frequency.
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OK, so it's all good fun, but why do you want to build a circuit which was a science competition project when I was in (primary?) school and that was a long time ago.? The transistors were supplied as a kit - germanium ones slightly more advanced than the OC71.
A 74HC14 can make six independent astable oscillators, one resistor and one capacitor each.