"Jeopardy" buttons debugging

[Magister]

Hi guys,

I built a "jeopardy" game buttons, meaning the first one that press his button, his light goes up even if the second one press his button.

Schematic is like this (even if it's in French, you can understand )
**broken link removed**
I couldn't find a 2N1711 (40 years old part?) so I used 2N2219.
Also instead of using 6V bulb I used LED, 3.2V.

I power the circuit with 3V, problem is, when I press button BP1 for instance, LED A1 light, but if I release the button, it goes off . Second problem is if I keep BP1 press (so A1 lit), when I press BP2, A2 lit too

I guess it's because the 2N2219 is not a good substitute , what could I use instead?

TIA all!

 

[Ubergeek63]

it is a combination of things...

it goes out because that circuit blocks but does not latch.

It lights a little because the LEDs are very sensitive and have a distinct voltage drop.

1Ks across the LEDs should get them to stay off.

SCRs would give you the latching action you want.

I think it could be tweaked a bit more still

 

[Boncuk]

Connect the base resistors directly to Batt+.

This eliminates unwanted glow of the LED not concerned.

Still no latching action, also no priority.

 

[pc88]

I think any general purpose NPN transistors can be used.

In addition to what Ubergeek suggests, it seems to me that one also needs to add series resistors to the LEDs to make the lockout mechanism work.

When lamps are used, pressing BP1 will turn on (saturate) T1. This not only causes current to flow through A1 (making it illuminate), but due to the resistive nature of lamps also drops the collector voltage of T1 to a small value like .2 V. At such a low voltage, T2 cannot be turned on by pressing BP2.

When using LEDs, however, the collector voltage cannot get lower than the supply voltage minus the LED voltage which in this case is 4.5-3.2 = 1.3V. This is more than enough to enable T2 to turn on when BP2 is depressed.

A solution is to add a series resistor to each LED. Something like 500 - 1K ohms should work.

 

[Magister]

I'll try it, thanks!