Calling all Circuit Wizards...

[nul-points]

all good points, gentlemen

when is a switch 'not a switch' - nearly always, it seems

and as you both suggest, it's the dynamics of the system that produce the interesting emergent features

and the interesting emergent feature of this system, as you've probably guessed by now,  is that the LED does indeed flash

not only that, the LED flashes when S1 gets switched to short-out the LED


for there to be any inductive kickback present, our 'switching' would have to interrupt current flow through L1 associated with C1

ok - so let's pull the 'ideal switch' apart and use flying leads, to give us a little more control over the 'switching' action

C1 appears to fully charge in less than a second and C2 takes a few seconds
(C1 charges to 1.24V, D1 is Schottky so C2 charges to approx 1V)

if we leave S1 in position 3 long enough, we can charge C1 fully and we can ensure also that C2 is fully charged - then there should be no current through L1 to interrupt when we disconnect S1 from position 3

let's also leave S1 totally disconnected for a few seconds - this should also ensure that any inductive kickback in the coil, in the charging phase, has passed

(i think we're being over-cautious here, but that in itself shouldn't be a problem)

ok, so now that current has ceased to flow through L1 - let's connect S1 to position 2 (S1-2)

what are we connecting?  we're establishing a short-circuit across the LED

(which as Gyula pointed out, has previously had the effect, together with D1, of ensuring that the voltage on C1 couldn't exceed around 3V)

so, by connecting S1 to S1-2, we're starting to establish a series connection for C1 & C2 (max. possible combined voltage is approx 2.4V) - we're also starting to clamp C1 with D1 (which will reduce combined voltage to approx 1.2V)

if the S1-2 connection experiences 'contact bounce' then one of two things can be happening at any instant:

a) S1-2 is closed:-
LED is shorted;
C1 is partially discharging shunted current via D1;
if the instantaneous voltage on C1 + C2 > 1.24V
  then some current will also flow back into the battery

b) S1-2 is open:-
LED is not shorted;
if the instantaneous voltage on C1 + C2 > 1.24V
  then some current will flow back into the battery


obviously current will only flow through the LED in its forward-biased direction, so the only circumstance when the LED might light is when the combined voltage on C1 + C2 > (1.24V + Vforward of LED)

Vforward of a white LED is likely to be >2V, so the combined voltage on C1 + C2 would need to be > 3.24V, and for a sufficient time to make a visible flash

we know that the combined voltage on C1 + C2 is approx 2.24V - which does not appear to be sufficient to light the LED

interesting

therefore some inductive kickback must be occurring in order to achieve a sufficiently high voltage to overcome the combined battery & Vforward voltages - but it can only be occurring on the recharge, not the charge cycle

so as poynt suggested in his update, a 'real' switch can have much more interesting effects than an 'ideal' one

a switch which we believed to be shorting a component out of a circuit can, under certain conditions, actually be causing the component to be significantly active (for a short period)

[osiris]

all good points, gentlemen

when is a switch 'not a switch' - nearly always, it seems

i wont  play in your thred .. i will add this

when a mechanical switch isint a switch  it is a   ........ ?

lol

a transmitter ... and a reciever ..



william