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Re: Need electronic expert advice for a project
Posted: Thu Jun 07, 2018 10:28 pm
by Pr0f
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.
Re: Need electronic expert advice for a project
Posted: Thu Jun 07, 2018 10:57 pm
by FrancoisLanciault
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
Re: Need electronic expert advice for a project
Posted: Thu Jun 07, 2018 11:27 pm
by 1024MAK
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
Re: Need electronic expert advice for a project
Posted: Fri Jun 08, 2018 11:12 am
by Pr0f
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