I'm still new and I'm still a beginner...
As an exercise I decided to build a simple timer - somewhat similar to 555.
My diagram is here:
The green block is my private "the 555 timer". It is expected to be in astable mode (output on/of periodically).
For the two comparisors I use a chip LM339AN.
The Flip-Flop I've made from two NOR-gates. To the left in the picture below.
Problem is that is doesn't oscillate. All I see is a permanent signal on the Q output (connected to an LED and via a 220 ohm resistor to ground).
In my trouble-shooting, I have partly disassembled the circuit, disconnecting the flip-flop.
At position A and B in the diagram I measure 5V and 3.3 V - as expected.
At position C, I only measure 1 V - this is a surprise to me; I expected 5 V. Don't think this is the only problem, however.
I have also tried installing two pull-down resistors at the flip-flop input - no changes..
If I move the transistor input from one side of the flip-flop to the other, the flip-flop changes state and becomes stable in this new position.
Oh, - a final remark of frustration.
Every time I try to build something electronic - even if I just copy something directly from YouTube - I always end up in hours of troubleshooting. Things doesn't work, ever, until hours of measurements and desperation has passed.
If it is only logic (SR-latch, binary adder) it is easier - but as soon as I add a transistor or a capacitor to a circuit Mother Nature turns angry.
It reminds me of the time when I learned to program - reading a book or watching the internet, I understood everything. Trying to code 5 lines myself and I was stuck. I did learn to code - and I will learn to build electronic circuits;but, Jesus, it is difficult and time consuming.
Back to my timer - all constructive input are welcome
As an exercise I decided to build a simple timer - somewhat similar to 555.
My diagram is here:
The green block is my private "the 555 timer". It is expected to be in astable mode (output on/of periodically).
For the two comparisors I use a chip LM339AN.
The Flip-Flop I've made from two NOR-gates. To the left in the picture below.
Problem is that is doesn't oscillate. All I see is a permanent signal on the Q output (connected to an LED and via a 220 ohm resistor to ground).
In my trouble-shooting, I have partly disassembled the circuit, disconnecting the flip-flop.
At position A and B in the diagram I measure 5V and 3.3 V - as expected.
At position C, I only measure 1 V - this is a surprise to me; I expected 5 V. Don't think this is the only problem, however.
I have also tried installing two pull-down resistors at the flip-flop input - no changes..
If I move the transistor input from one side of the flip-flop to the other, the flip-flop changes state and becomes stable in this new position.
Oh, - a final remark of frustration.
Every time I try to build something electronic - even if I just copy something directly from YouTube - I always end up in hours of troubleshooting. Things doesn't work, ever, until hours of measurements and desperation has passed.
If it is only logic (SR-latch, binary adder) it is easier - but as soon as I add a transistor or a capacitor to a circuit Mother Nature turns angry.
It reminds me of the time when I learned to program - reading a book or watching the internet, I understood everything. Trying to code 5 lines myself and I was stuck. I did learn to code - and I will learn to build electronic circuits;but, Jesus, it is difficult and time consuming.
Back to my timer - all constructive input are welcome