How to construct a discrete circuit to send out a square wave with N pulses?

Question

I want to build a simple and discrete circuit (without any integrated circuits) which puts out a square wave (50:50 duty cycle) with N pulses (rising edges)?

For example for N=4 the output should look like this:

The time of one period (from rising edge to rising edge) might be in the range of 10 - 100 ms.

Any ideas how to achieve this?

I thought on using a capacitor, which charges and puts out a square wave and another capacitor which "enables" (AND gate?) the signal and is sized the way that it enables as long as 4 pulses take. But I've no idea if this is even possible ...

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Here are some more details:

• The circuit should be discrete: using only transistors, resistors, capacitors (no "complex" devices/ICs)
• The N is fixed, meaning that there is a N=4 circuit which generates 4 pulses on button press
• "... good old dialphone's mechanical approach" - I've looked it up and this is what I want but not mechanically but electronically
• "What is the maximum number of pulses you want to create, and how do you want to set the count?" N ranges from 1 to 9 and the circuit is built for N, so it is not variable.

Answer 1

Thinking outside the box:

An astable multivibrator that has a diode and cap on the output. When the pulse is high it charges the cap a little bit. After N pulses the voltage will reach a threshold which is detected by a comparator, and that disables the multivibrator.

You'll need a method to reset it by discharging C1 as well.

Here is a conceptual diagram:

^{simulate this circuit – Schematic created using CircuitLab}

Answer 2

Use a monostable multivibrator to "gate" an astable multivibrator:

^{simulate this circuit – Schematic created using CircuitLab}

Adjust R5 and R6 for the frequency and duty cycle of the pulses. Adjust R7 for the number of pulses.

Here's a simulation result showing 4 pulses at 10 Hz each time the trigger fires.