74190 counter problem

Question

So, I got my 74190 counter shows number like this 9-8-7-6-5-4-3-2-1-0-5-4-3-2-1-0-5-4-3-2-1-0-5-4-3-2-1-0 and so on.

My questions:

What can I do to change the output count down into 5-4-3-2-1-0-5-4-3-2-1-0 and so on?
When it changes 0 into 5 it moves so fast. How could I fix this one?

the output of U8A is short-circuited by the switch S3. move the switch into the input circuit of U8A. — Jasen Слава Україні, May 04 '18 at 10:40
the schematic could be improved by simplifying the ground net so that ground wires do not cross other ground wires. — Jasen Слава Україні, May 04 '18 at 10:43
i dont know about how to move switch into the input circuit of u8A because it causes error on my circuit :( — Evangelina Tessia P, May 04 '18 at 11:48

score 1 · Answer 1 · edited May 05 '18 at 01:04

1

You cannot predict the initial state of the counter.

You must make a reset circuit that brings the counter to a known state at powerup.

Replace U8A with a NOR gate with one pin to an RC reset circuit or you can use a spare OR gate with U8A to make a NOR gate:

schematic

^{simulate this circuit – Schematic created using CircuitLab}

On powerup the capacitor will drag the second input to "1" for a short time forcing a a counter load. This will make the counter start from 5.

From the additional comment I understand that the technology used is really LS which has an 1 mA input current, I thought it was just the schematic.

A fix is to use a negative reset like this:

schematic

R can be higher that 2k2 since the input high current is of uA order and also the capacitor if the reset does not work properly

edited May 05 '18 at 01:04

Hearth

answered May 04 '18 at 11:06

Dorian

But, it makes counter goes from 5-4-3-2-1-0-9-8-7-6-5-4-3-2-1-0-9-8-7-6-5-4-3-2-1-0-9-8-7 so on :( – Evangelina Tessia P May 04 '18 at 11:45
How can be possible ? With the reset input to '0' it should act as an inverter as in the original schematic. Are you sure you wired the MAX/MIN output to the gate? – Dorian May 04 '18 at 11:58
@EvangelinaTessiaP You actually use the old 74LS version , not 74HC or 74HCT version? – Dorian May 04 '18 at 12:04
Yes. I use the old 74LS version – Evangelina Tessia P May 04 '18 at 12:27
@EvangelinaTessiaP Oh, I didn't know that are still used, the LS have a higher input current that make the voltage on R to be higher than input low level. You should use a negative reset, i will update my answer right away – Dorian May 04 '18 at 12:50
@EvangelinaTessiaP Did it worked? – Dorian May 11 '18 at 11:40
well sorry for not informing you. I'm using ic 74169 instead if ic 74190. Because it works well and more easier than ic 74190. Thank you for your help. – Evangelina Tessia P May 11 '18 at 11:44

1 Answers1