Double duty pin?

[212]

If you have read any of my posts so far you know I'm all about lights, cameras and RF

I have run out of pins on my on-going RF video project. I'm using the 08M chip. I have pin3 for input...good. I have to turn on an A/V transmitter...OK...one output pin. I need to send a tone to control my VCR operation on the receive end of things....fine....two pins. I need to turn on an IR LED array if it is needed...three...and I need 2 pins to know if it is needed...one to power the CDS and one to read it. OH yeah...camera too!...make that triple duty, I'll have to wire the camera and transmitter to power on at the same time as the CDS...

Question is: anyone see a problem using the same pin to turn on a mosfet to power my RF transmitter and camera and use the same pin to power the CDS??? I think I know, but I hate to keep re-doing stuff that don't work

 

[moxhamj]

Been there many times! Then I went and bought some 14Ms and now have spare stock of both 08Ms and 14Ms. They are pin for pin compatible, so if an 08M runs out of pins, just download the code to a 14M. Build boards with 14 pin sockets and either put in an 08M or a 14M. Sometimes a project starts in a 14M and ends up in an 08M.

I know that doesn't quite answer the exact question - sorry.

 

[hippy]

The biggest problem you'll encounter is that using one pin to turn everything on means just that; everything is either on or everything is off.

If that's not a problem then all welll and good, but if you are running on batteries you might want to only power things up when you have to and only keep them on for as long as is necessary to extend battery life. You may also need to go to a 'chunkier MOSFET' because it will have to be able to handle the entire maximum worse-case current draw, and turning everything on together can cause in-rush current problems if you have some high draw components.

The 14M's are only slightly more expensive than 08M's so Dr Acula's idea is a good one.

 

[212]

I been asking myself if it might be time to move up to a bigger chip. One problem with that is, I put all my chips facing in a way where I don't have room toward the end the extras would be....doh! I been thinking about the mosfets too, thinking I can still use separate ones for each load, just power them all on with one pin. Yes, it will be battery powered, but all total it uses near 2 amps anyway, so the little extra used for checking for daytime does not bother me much. Hey...thanks for the replies!

 

[manuka]

You may as well go for broke & move all the way to a "10 a side" 20M, as these have 8 inputs & 8 outputs. Cost is only about US $1 more.

 

[212]

OK...now you are scaring me!

 

[inglewoodpete]

212, You can get some clearance for a 14M chip in an 08M socket by getting a 14-pin socket and an additional 8-pin DIP socket. Since the 1st or 'top' 8 pins are 1-for-1 compatible between the 2 chips, the 14M can be inserted into the 'stacked' sockets.

The additional 6 pins from the 14-pin socket can be soldered to flyleads.