BS2 expanding the number of outputs

Mark Dietrich

I am thinking of being able to create 15 outputs from 8 outputs by using 2-input AND gates and having them trigger a ULM 2803, ( 8 darlington pairs), having them drive small relays. I figure if I use (2) outputs to create one, I can use 1 and 2, 1 and 3, 1 and 4, 1 and 5, 1 and 6, 1 and 7, 1 and 8, 2 and 3, 2 and 4 ,etc to 7 and 8. Is this a standard way of doing this type of thing? I have experimented with the ULM2803 and it works great for driving relays.

TinkersALot

Try a decder for this. 74hc154 comes to mind

Mark Dietrich

Thanks, TinkersALot. I thought that I invented something new. Have downloaded the spec sheet and now have to try to understand it. It's like, $1.70 and looks promising. I just happen t have a whole BIN of quad 2-input CMOS AND gates lying around. I just breadboarded the concept and it works great. It may be stupid to do, though if there is a $1.70 solution. Thanks again.

Mark Dietrich

I just did a little math and discovered that if I use e 74HC154, I can consume 12 BS outputs to get 48 outputs, but using the AND gates, I can get 66 inputs from the same 12 BS outputs. Is there another device that will match this gain? I probably should not have posted until I really understand the 74HC154 suggestion better. I learned a lot from TinkerALot in any case. A new tool for my toolbox.

Tracy Allen

One popular way of doing this is with the 75HC595 shift register. It takes 3 pins from the Stamp to get 8 outputs. Moreover, the chips can be cascaded so that the same three pins can serve for 8, 16, 24, 32, 40, 48 etc outputs. The data is shifted out in serial form using the SHIFTOUT command. You can find a circuit in the Stamp manual on the SHIFTOUT reference pages, and you can find how to cascade multiple chips in StampWorks (download from Parallax.com).

There are industrial relay drivers that have 32 outputs per 40-pin package with darlington power drivers included, also used with SHIFTOUT, for example, here.