Bus Switcher with Counter

[emailer33]

So this is my first time trying to come up with a decent circuit myself, and I was hoping someone could help me come up with what would be the best way to do this.

I'm using the A/V switcher tutorial on engadget that uses a 8-bit TTL bus switcher. I'm going to have 5 of them, and rather than control them all with push switches, i wanted two momentary switches and a counter display. I figured a modulo-5 setup with a 74ls90 was the best route after reading some simple circuits, but I have no idea how to set up the 7490 for a modulo-5 setup, nor having a way of enabling just one switch per number.

So what would be a good way to do this, and is there anything I should really watch out for?

 

[AllVol]

So what would be a good way to do this?

I have read the engagdet article. It seems pretty straightforward. Let me see if I understand the problem:

You want one pushbutton that will advance a counter from 1 through 5, and upon reaching a certain number, the other pushbutton will select and activate the corresponding bus switch. Is that basically it?

 

[emailer33]

I'm sorry, actually I just want two push buttons to control a counter, one to advance it, the other to decrease it, I want the bus switch to be activated as soon as the number is changed.

 

[ericgibbs]

hi,
The 74LS90 is only an up counter, it can be configured to count as a '5' counter,
but if you want to select '1 of 5' you will have to use a decoder ic.

Have you looked at the HEF4017, I know its only a up counter, buts its from 0 thru 9.
Use 0 to 4 for your selection and reset to 0 on the next switch push which is output 5.

In other words it loops round 0 thru 4 to 0

Hope this is useful, let me know, there are many options.

Eric

 

[emailer33]

Thank you for the help, but I have decided to stick with the 74LS190. I've also did a little more looking and I think i'm going to use a 74LS145 and just use hte first five digits to control the bus switches. Hopefully it works out well, thanks again.

[edit] bah scrap that, while the 190 works great in multisim, i can't find the part.

 

[AllVol]

Thank you for the help, but I have decided to stick with the 74LS190. I've also did a little more looking and I think i'm going to use a 74LS145 and just use hte first five digits to control the bus switches. Hopefully it works out well, thanks again.

For your information, the 74LS145 is a BCD to decimal decoder, which means it translates a binary number into a decimal number. To get the binary, you need something like a 74LS90 to translate switch pushes into binary.

Actually, I think Eric had the right idea. A cd4017 could be individually pulsed with a switch, and looped through to five positions, but would eliminate the binary to decimal decoding.

With either system, if you want to go backwards, you will be faced with having to go forwards through the loop to get where you want to be.

 

[emailer33]

oo ok. multisim said the 145 was a bcd to decimal conv, and it worked in the simulation. Well i'll continue to look into the CD4017, although I will say its begininng to look mroe complicated to me than its worth.

 

[AllVol]

although I will say its begininng to look mroe complicated to me than its worth.

Ah, yes.

Of course the multisim is going to show a working arrangement, because when you connect the ABCD inputs the sim assumes that is a viable binary number, and will proceed. Try it with no connections to ABCD, or leave just one off, and see what happens.