What's the correct way to make an I/O Pin bridge a jumper?

Phil.B

I have searched the forums and have not managed to find a post that totally lines up with what I am attempting to do. I apologize if this a silly question, but I have been messing with this project for the last 10 or so hours and I seem to be at a loss.

I am interfacing a RF remote control unit with my propeller and I have successfully wired and programed the ON and OFF buttons which simply required 3v to activate them and ground to deactivate them. These remote buttons are fully controllable by using code on the prop now and work great. However, I am now stuck with how to activate the RF channel select jumpers. The channel selector is made up of 3 solder pads on the board that you connect to ground in order to select channels 1 through 3 with the 4th channel being selected by all jumpers being open.

Currently for testing I have soldered jumper wires to these channel select solder pads and I manually move the wire for the channel I want to common ground on my board bypassing the propeller which works. The part that was confusing me is the jumpers need to be unconnected to anything else when not in use and all jumpers must be open to select channel 4. I know this can be done with a relay, but I am pretty sure there is a much easier way to do it with a few resistors and maybe a transistor or two that is simple enough to just connect a jumper wire to ground sending no voltage over it at all via a propeller I/O pin.

Thanks in advances and I am sorry if any of this post was confusing. I will clear up anything that is fuzzy as soon as I wake up tomorrow, so please let me know if it needs further explaining or pictures.

-Phil

Phil Pilgrim (PhiPi)

Phil,

What is the voltage on the jumper pins when they're not grounded? If it's less than 3.6V, you can connect Prop pins directly to them, and use DIRA to pull them down or release them. If it's more than 3.6V, you can use NPN or nMOSFET transistors to do the switching for you.

-Phil

Phil.B

Thank you for the super fast reply! I went to lay down in bed and saw the email now here I am measuring voltage on solder pads

When they are not grounded the voltage is around 16mV on the jumpers and that thought had crossed my mind before. However, my fear was that while setting the pin to 0 will select the channel I want wouldn't setting it to 1 push 3.3v from the propeller on the jumper possibly damaging my RF remote control board? I am not 100% sure what I can put through that jumper connection voltage wise without making it go poof. Again I fear it might be my VERY over tired mind at work, but would you happen to have a simple wiring diagram on how to connect the prop pin and protect the jumper from too much voltage or a code snip that you could share? I am sure it is so dead simple I will have to do face palm in the morning, but I am 99% finished interfacing this remote and I would really hate to jump the gun and smoke something. I guess it is better to ask a silly question than to nuke the device

markaeric

Phil,

It seems pretty strange that you're only seeing 16mV at the pads. Perhaps there are some diodes prior to the pads? You can try using a low value resistor between the pad and ground, and check to volatge at the resistor's terminals, to see if it's still 16mV.

If you tie the pads directly to the prop pin, you might be ok if you make sure you never set the pin high... When you don't want the pad grounded, you would set the prop pin as an input, which will put it in a high impedance state, which would make it look like no jumper is there as far as the pads are concerned.

Toby Seckshund

As Phil said, if the supply to the RF bits are definitely never going to give out more than 3.3 Volts the by setting a pin to input effectively sets it to a high impedance that will be as good as the open circuit pads. When set to an out with a low output state then it will be as shorted pads.

This assumes that the pads are from some pull up down to ground, check that the pads are so and not some form of "keyboard matrix" of other ins and outs.

Phil.B

As promised I do feel a bit foolish because I read the idea of using DIRA as OUTA like I use to control my buttons. I will double check the solder pads and attempt to activate with DIRA then report back. I would also like to thank everyone for the helpful info and for dealing with my over tired rambling.

Phil Pilgrim (PhiPi)

Phil,

16 mV is really low. Did you measure between the pin and ground? What kind of meter did you use to take that measurement? Do you have a scope you can use to examine the pins? I wonder if those pins have AC on them instead of DC. If so, that changes things a bit.

-Phil

Phil.B

It worked like a charm directly wired to a pin set an input pin like you said. I rechecked the voltage again after some sleep and got a much better reading of about 0.67 volts. I think I may of had one of the jumpers turned on which could of hosed up my reading, or maybe it was the fact that I felt like my eyes were about to fall out of my head when I measured it the first time at 2am

To sum it all up I have the 3 jumpers connected to pins 3 through 5 and by using DIRA to set all pins to be inputs I can access channel 4. When I want to access another channel I use OUTA to pull the needed pin low and it seems to be working well so far. I have used a very crude proof of concept code to successfully switch on a test lamp and all of my fish tank lighting which is located on two separate RF Channels (1 & 4) via the Parallax Serial Terminal with text commands and my single hacked remote unit. The next step will be to neaten up my tangled mess of jumper wires and get a cleaner version of my control code for further testing. I have plans to add a mini web server into this project to allow me to extend the reach of my RF remote to anywhere I have internet access and my phone. So far the results are pretty promising for a simple 110v Christmas light control system I grabbed for $7ish each last year on clearance at Home Depot/Lowes

Thanks again for the help everyone.