Firstly, I will point out two problems.

Someone replaced the original gates with 74LSxx series gates.
CD4000 series gates use CMOS technology.
74LS00 series gates use BJT technology.
They have very different characteristics and you cannot interchange the two without making adjustments.

PRE and CLR inputs on 74LS74 are active LOW. That is a dead give away why this circuit will never work.

Thanks. In post #13 of my "Gate Control For Frequency Counter" thread someone said that you could
replace the CMOS devices with TTL. I want to use TTL as I currently have no CMOS devices. What adjustments
are required to implement this circuit using TTL?

 

Thanks. In post #13 of my "Gate Control For Frequency Counter" thread someone said that you could
replace the CMOS devices with TTL. I want to use TTL as I currently have no CMOS devices. What adjustments
are required to implement this circuit using TTL?

You can do that as long as you don't mix and match TTL with CMOS.

 

Thanks. In post #13 of my "Gate Control For Frequency Counter" thread someone said that you could
replace the CMOS devices with TTL. I want to use TTL as I currently have no CMOS devices. What adjustments
are required to implement this circuit using TTL?

In this particular circuit here are the things that need attention.

1) Chip pin numbers will be different. Check the pinout for 74LS74.

2) PRE and CLR use negative logic, i.e. they require logic 0 to activate the function. Connect both of these to +5V.

3) 74LS00 series gates require more current on input pins than CD4000 series gates. A 10kΩ resistor will not pull an input low. You need about 220Ω. The purpose of the C and R is to convert a rising edge to a single shot output. You will have to twiddle with these components in order to get it to work. Do you have access to an oscilloscope? This will allow you to observe exactly what is going on.

A more reliable way of generating one-shot pulses is to use a monostable multivibrator such as 74LS123.

 

If you want to continue to use the 74LS00 and C-R differentiator I would switch to generating a pulse on the falling edge. This will allow you to use higher values of R.

I can show you how to do this.

 

If you want to continue to use the 74LS00 and C-R differentiator I would switch to generating a pulse on the falling edge. This will allow you to use higher values of R.

I can show you how to do this.

Thanks MrChips. I will switch to generating a pulse on the falling edge if you can show me how to do this.

 

Sorry. When I said 220Ω pulldown resistor I was thinking 7400 series gates.
7400 series input LOW current is -1.6mA max.
74LS00 series input LOW current is -0.4mA max., four times lower.

You can use 1kΩ pulldown resistors for R1 and R2.

 

Sorry. When I said 220Ω pulldown resistor I was thinking 7400 series gates.
7400 series input LOW current is -1.6mA max.
74LS00 series input LOW current is -0.4mA max., four times lower.

You can use 1kΩ pulldown resistors for R1 and R2.

Here is what I have now but it doesn't work.

 

Do you have access to an oscilloscope?
If not then you will have to improvise and sharpen your trouble shooting skills.

Here is how you can improvise.
Wire up a spare counter chip, 0-15 counter or 0-9 counter will do.
Connect LEDs, or 7-segment display or even use the highest digit of your counter circuit for now.
Use the clock input of the counter as your probe. You want to see if your test counter increments and therefore recognizes the presence of clock pulses. Start with the output of the 74LS74 and work your way through all the 74LS00 gates.

 

Do you have access to an oscilloscope?
If not then you will have to improvise and sharpen your trouble shooting skills.

Here is how you can improvise.
Wire up a spare counter chip, 0-15 counter or 0-9 counter will do.
Connect LEDs, or 7-segment display or even use the highest digit of your counter circuit for now.
Use the clock input of the counter as your probe. You want to see if your test counter increments and therefore recognizes the presence of clock pulses. Start with the output of the 74LS74 and work your way through all the 74LS00 gates.

If I disconnect this circuit, the counter will count to 99999.

Pin 5 of the 74LS74 has a pulse output of 1 hz. Pins 3, 6, and 8 of 74LS00 are at logic "1" and pin 11 is at logic "0".
I guess the 74LS74 is functioning normally and the problem is with the 74LS00?

 

What are you using to perform these tests?
You cannot use an LED because the duration of the pulses are of the order of 1μs and too short to observe on an LED.
You need a circuit that will respond to pulses.

 

What are you using to perform these tests?
You cannot use an LED because the duration of the pulses are of the order of 1μs and too short to observe on an LED.
You need a circuit that will respond to pulses.

View attachment 225143

Hi:

I have probed various points with a Tektronix 1052B scope and I attached the results. The scope only measures down
to 10 Hz.

 

Tektronix 1052B oscilloscope is a digital scope. You can record single shot events down to DC.
Set your scope to NORMAL trigger or SINGLE trigger and look for a single event.

Another way of testing your circuit is to use a faster clock signal into the 74LS74 flip-flop to give you higher repetition rates on the oscilloscope. Trigger the scope on the output of the 74LS74 flip-flop on CHAN 1 and look at the outputs of the C-R one-shot circuits on CHAN 2.