The Sinclair QL Forum

This makes more sense now on the switch side of things.

The switch enable will trigger that lower of the 3 comparator's (there are 4 in the 339 package), and that in turn will switch Q6 on, allowing the SW pin to rise towards +12V, it would normally be dragged to 0.6V by the bias resistor to -12V and the action of the lower protection diode on the SW input, the 2 diodes here normally just pass any unsavoury voltage spikes to ground or +12V line.

So when enabled, the SW input will have a nominal positive voltage, but at rest -0.6V

The remaining 2 comparators in the circuit act as a window comparator, providing some hysteresis for the switch action, and toggling the JK flip flop.

Pr0f wrote:This makes more sense now on the switch side of things.

The switch enable will trigger that lower of the 3 comparator's (there are 4 in the 339 package), and that in turn will switch Q6 on, allowing the SW pin to rise towards +12V, it would normally be dragged to 0.6V by the bias resistor to -12V and the action of the lower protection diode on the SW input, the 2 diodes here normally just pass any unsavoury voltage spikes to ground or +12V line.

So when enabled, the SW input will have a nominal positive voltage, but at rest -0.6V

The remaining 2 comparators in the circuit act as a window comparator, providing some hysteresis for the switch action, and toggling the JK flip flop.

Well I am not sure I understand everything, but I am glad you do!

In light of these latest information, what is the good orientation of the Q7 transistor ?

Once the Q7 transistor orientation is clarified, I will built and test the light pen. Obviously I will report the outcome here!

Thank you again.

François

FrancoisLanciault wrote:

Pr0f wrote:This makes more sense now on the switch side of things.

The switch enable will trigger that lower of the 3 comparator's (there are 4 in the 339 package), and that in turn will switch Q6 on, allowing the SW pin to rise towards +12V, it would normally be dragged to 0.6V by the bias resistor to -12V and the action of the lower protection diode on the SW input, the 2 diodes here normally just pass any unsavoury voltage spikes to ground or +12V line.

So when enabled, the SW input will have a nominal positive voltage, but at rest -0.6V

The remaining 2 comparators in the circuit act as a window comparator, providing some hysteresis for the switch action, and toggling the JK flip flop.

Well I am not sure I understand everything, but I am glad you do!

In light of these latest information, what is the good orientation of the Q7 transistor ?

Once the Q7 transistor orientation is clarified, I will built and test the light pen. Obviously I will report the outcome here!

Thank you again.

François

Emitter goes to GND.

Mark

1024MAK wrote:

FrancoisLanciault wrote:

Pr0f wrote:This makes more sense now on the switch side of things.

The switch enable will trigger that lower of the 3 comparator's (there are 4 in the 339 package), and that in turn will switch Q6 on, allowing the SW pin to rise towards +12V, it would normally be dragged to 0.6V by the bias resistor to -12V and the action of the lower protection diode on the SW input, the 2 diodes here normally just pass any unsavoury voltage spikes to ground or +12V line.

So when enabled, the SW input will have a nominal positive voltage, but at rest -0.6V

The remaining 2 comparators in the circuit act as a window comparator, providing some hysteresis for the switch action, and toggling the JK flip flop.

Well I am not sure I understand everything, but I am glad you do!

In light of these latest information, what is the good orientation of the Q7 transistor ?

Once the Q7 transistor orientation is clarified, I will built and test the light pen. Obviously I will report the outcome here!

Thank you again.

François

Emitter goes to GND.

Mark

What he said