Discussion in 'The Projects Forum' started by dyeraaron, Nov 10, 2008.

1. ### dyeraaron Thread Starter Active Member

Oct 27, 2008
57
0
I have a 555 Timer tuned in at 2 Hz according to 1.44 / R1 + (2)R2 (C) whose output goes into pin 14 of a 7490 decade counter. the decade is cascaded into a 7493 Binary counter which goes to 7447 decoders to drive 2 segment displays to count up.....my question is pin 14 I was talking out on the 7490 is CLK "A" input.....pin 1 is CLK "B" is that my input from lets say a frequency generator so my circuit will actually count?

2. ### beenthere Retired Moderator

Apr 20, 2004
15,815
283
I can't really follow your explanation. To get the 7490 counting, apply the 555 pulse to pin 14, and tie pin 12 to pin 1. That will let the counter do a divide by 2 anf a divide by 5. To get the 7493 counting properly, you will need to sense when the 7490 has gone to 0000 and clock it then.

3. ### mik3 Senior Member

Feb 4, 2008
4,846
63
This a piece of text in the datasheet here:

http://www.engineer.gvsu.edu/students/part_inventory/dm7490an.pdf

To use the maximum count length (decade or four-bit
binary), the B input is connected to the QA output. The
input count pulses are applied to input A and the outputs
are as described in the appropriate Function Table. A symmetrical
divide-by-ten count can be obtained from the
counters by connecting the QD output to the A input and
applying the input count to the B input which gives a divideby-
ten square wave at output QA.

4. ### dyeraaron Thread Starter Active Member

Oct 27, 2008
57
0
I did tie pin 1 into pin 12 and studied the logic on the datasheet....I jumpered pin 3 which is RO(2) to GND to get the Low. I put the O scope on it and they count but I don't get why my segment displays wouldn't...I did however tie some highs and lows into my 7447s for that logic. Sorry for the schematic...I don't have multisim or a scanner where I am on this computer...although I did draw it.