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Wait 5"
Sometimes, depending on the configuration, you can see artefacts over the waves or maybe, the circuit don't want to do what it must to do. If this happens, try it moving faster your smartphone during 2" because this create noise into the circuit.
My initial configuration works fine.
From left to right:
R1, R2, R3, R4
C1, C2
T1, T2
Nomenclature:
BE Base-Emitter
CE Collector-Emitter
Beta = 300
HOW IT WORKS
Due to the components are not exactly equal, the circuit goes to unstable state. In one moment T1 is in saturation and T2 is in cut-off.
So T2 is in cut-off mode, T2Vce = Vcc and C2 charge through R4 and T1(BE). This current through T1(BE) takes T1 to saturation. So T1Vce ~0, C1 discharge its little charge through R2 and T1 (CE)
When C2 is full charged the current through T1(BE) disappear and T1 goes out the saturation mode. C1 begin to charge and due this, a current flow through T2(BE) taking T2 to saturation. Due this, a negative pick appears in T1(B) that takes T1 to cut-off quickly. Now is C1 who charge through R1 and T2(BE). This current takes T2 to saturation. Now C2 can discharge through R3 and T2(CE). So T2 Vce~0, we can say that in the base of T1 there's -V(C2).
This ensures that T1 is in cut-off mode. The exponential curve (green) is the discharge of C2.
Blue is T1 Vce
Orange is discharge of C1
If you want to build this one, you need to know how calculate the timing of two cycles.
R1 and R4 are not used.
- Time for active cycle on T1 are controlled by R3 and C2
- Time for non active cycle on T1 are controlled by R2 and C1
T = R*C*0.7 seconds
Remember to add two times and that frequency is inverter of time.
Example:
T1 = T2 = 300000 * 0.0000005 * 0.7 = 0.105s
T1 + T2 = 0.21s
F = 1/ T = 1 / 0.21s = 4.76Hz
You will need adjust time factor (0.7) to get the best result.
PS:
C1 & C2 discharging could be seen too as C1 & C2 charging from -10v to 10v. That's the reason why de Tau factor is 0.7 are not 5. The factor 5 is for a 96% of a charge/discharge RC circuit.
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