Need electronic expert advice for a project

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Pr0f
QL Wafer Drive
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Re: Need electronic expert advice for a project

Post 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.


FrancoisLanciault
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Re: Need electronic expert advice for a project

Post 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


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1024MAK
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Re: Need electronic expert advice for a project

Post 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


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QL, Falcon, Atari 520STFM, Atari 1040STE, more PC's than I care to count and an assortment of 8 bit micros (Sinclair and Acorn)(nearly forgot the Psion's)
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Pr0f
QL Wafer Drive
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Joined: Thu Oct 12, 2017 9:54 am

Re: Need electronic expert advice for a project

Post 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 :-)


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