Why is my D-latch not working?

michael8

Joined Jan 11, 2015
472
The underlying point of "gate" design is the assumptions that gates have standard input and output levels. That "AND" gate's
output levels doesn't match the input levels your NOR gates depend on. The output needs to be close to ground for
a low input and close to Vcc for a high. The 2 1K resisters in series (assume an unreal 0 volt drop across both transistors)
leaves the output about 1/2 Vcc.

This is "logic gate design", not "logic gate use".

I'm not sure how much understanding you have of ohms law and transistors. Can you measure the voltages
on your circuit? You might learn a lot by measuring the voltage at the gate outputs and inputs (and transistor base voltages).

More on historical logic gate families: (Your NOR is a version of RTL resistor transistor logic)

https://en.wikipedia.org/wiki/Logic_gate
https://en.wikipedia.org/wiki/Resistor–transistor_logic
https://en.wikipedia.org/wiki/Diode–transistor_logic
https://en.wikipedia.org/wiki/Transistor–transistor_logic
https://en.wikipedia.org/wiki/CMOS
 

Thread Starter

Ajgor

Joined Nov 16, 2023
16
The underlying point of "gate" design is the assumptions that gates have standard input and output levels. That "AND" gate's
output levels doesn't match the input levels your NOR gates depend on. The output needs to be close to ground for
a low input and close to Vcc for a high. The 2 1K resisters in series (assume an unreal 0 volt drop across both transistors)
leaves the output about 1/2 Vcc.

This is "logic gate design", not "logic gate use".

I'm not sure how much understanding you have of ohms law and transistors. Can you measure the voltages
on your circuit? You might learn a lot by measuring the voltage at the gate outputs and inputs (and transistor base voltages).

More on historical logic gate families: (Your NOR is a version of RTL resistor transistor logic)

https://en.wikipedia.org/wiki/Logic_gate
https://en.wikipedia.org/wiki/Resistor–transistor_logic
https://en.wikipedia.org/wiki/Diode–transistor_logic
https://en.wikipedia.org/wiki/Transistor–transistor_logic
https://en.wikipedia.org/wiki/CMOS
Electronic is just my hobby, the next year i will go to univeristy for electical engereering :) I am also not engilsh so i have trouble learning on my own, but i will check theese links.
 
Last edited:

dl324

Joined Mar 30, 2015
18,336
Electronic is just my hobby, the next year i will go to univeristy for electical engereering
It seems to me that you're using a lot of transistors when something like this would work:
1700519736499.png
Can't remember if I ever breadboarded the circuit because I decided to go with R#S# because it simplified the counter logic, and I used BC547. I used the simulator between my ears to convince myself that it would work...
 
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