Cellphone remote switch

[Greg Arehart]

Here's what I've been doing when I can't do any test flying....

A couple weeks ago I posted a request here regarding build-your-own remote cellphone-operated switch to turn on my engine heaters remotely. I finished putting this together tonight. Total cost about $50 as follows:

$11 - 4 x 6 x 6 plastic junction box from Home Depot (includes a sealable waterproof lid!)
$18 - Apogee kit (http://www.apogeekits.com/remote_con...cell_phone.htm) including shipping
$10 - cheap walmart cellphone, comes with 10 minutes (good for 30 days)
$20 - optional additional minutes, good for 90 days



This photo shows the wiring inlet - standard electrical fixture (I got a waterproof one, but unless this is outside, waterproof is probably not necessary)



This is the assembled kit, which I screwed to the bottom of the box with 4 screws in the corners of the board.



Closer view of the board. Ignore the orange piece of tape - it shouldn't be there. Large blue box is the relay - rated at 15 A 110 V so should handle most any engine pan heater and/or cylinder heaters (my setup totals 500 W). 110V wires are connected to the common and NO (normally open) points. Red thing is the potentiometer to adjust the sensitivity of the photocell. Photocell is the little thing sticking up from LDR1. It can be bent to whatever orientation is necessary. DC power for the board is on the right (SK2) - I used an old power supply from a telephone or something, but make sure it is 12V and not something else. The board comes with a plug for the "standard" 12V circular plug, but I wired mine direct because of space considerations. Everything else is just put on the board per the instructions in the kit.



This is the same view with a small shelf I manufactured out of scrap Al (lots of that left around the shop!). The photocell is in the center below the hole. I will just put my cell phone on the shelf and hold it down with a couple rubber bands. The key is to make sure you get a phone that lights up CONTINUOUSLY when you call it, and place the screen so it faces the photocell. Adjust the sensitivity so the light from the cellphone triggers the relay consistently. Mine is set to high sensitivity because there is no other light that can enter the box so I am not worried about extraneous triggers. By the way, there are two modes on the circuit board. Mode one is where a single call switches the relay on for a preset amount of time up to an hour. Mode two requires two calls (in close succession) to the phone to switch it on, and it stays on until a third call is made, which switches it off. The small USB-style plug in this photo is cell phone power.

Other notes. I just took some RTV and glued the two transformers (one for the circuit board, second for the cell phone) into the corners of the box. I soldered pigtails onto the plugs for these transformers to make them easy to wire (see figure 2 above). For the power cords, I just cut an old extension cord in half.

All in all, a pretty easy and cheap way to remotely turn on my heater! The only drawback is the cell minutes. Since I never answer the phone, I don't use any minutes, but they expire after a certain time, so I'll have to get more minutes next winter. I am hoping I can find a better/cheaper deal on minutes than the $20 cards that I see.

If anyone needs more details, feel free to PM me (I will be out of town all next week, however).

cheers,
greg

[vansrv8]

Wow, we both basically did the same project in the last week, but I used a different board. I picked up an 8 channel DTMF controller from NHRC. This one uses the phone DTMF codes to turn up to 8 things on/off and has password protection and transmits an acknowledgment in morse code...
http://www.nhrc.net/nhrc-remote-plus/

I set it up with two relays, one channel for the preheat and another for the battery charger. Sure saves driving out to the field and waiting for a couple of hours!

[Lycosaurus]

Originally Posted by vansrv8

...This one uses the phone DTMF codes to turn up to 8 things on/off ...

... and it works? Reason I ask, is that cell phone audio is a highly compressed digital stream, which has difficulty transmitting audible DTMF... or at least that is my understanding.

[vansrv8]

..it does with the samsung phone that I am using .. YMMV

[whifof100ll]

Originally Posted by Greg Arehart

Here's what I've been doing when I can't do any test flying....

Large blue box is the relay - rated at 15 A 110 V so should handle most any engine pan heater and/or cylinder heaters (my setup totals 500 W). 110V wires are connected to the common and NO (normally open) points. cheers,
greg

Greg,

I did essentially the same thing you did, with one difference that might be important. While the relay on the board is rated for 110V, the circuit board runs are not. The circuit board is indeed rated at a max of 24V and is marked as such.

The solution is to use a simple external relay. I ran a jumper wire from the power pin to one of the NO pins on the board, then used this to power the coil to an external control relay ($7). Might not be an issue, but electrically 110V is not kosher for the circuit board on the kit you are using. (read fire + hanger = )

BTW, I am using the dip switches set up where call it twice to turn on, and once to turn off. I have been using it for a few months now and it works well. Just put your phone on the do not call list so that a junk call does not turn off your preheat.

[Greg Arehart]

Dale,

The board itself is powered by 12V and the relay is isolated from the rest of the board and is designed for switching 110V. My electrical guy in my lab tells me that it should not be an issue - and the Apogee folks clearly show it turning on and off lights, so I am not too worried. Never hurts to have an extra layer of protection, however.

cheers,
greg

[MikeT]

Greg, I built the same Velleman kit that you built and put the additional relay to handle the current of the heater and put it out at the hanger. It worked when I put it out there, but wouldn't work when needed. I did some research and one of the two IC's quits working at 32 degrees f. I see you live in NV. so you might be OK, but here in Michigan it doesn't work a good part of the winter. I also tried putting one of those heaters they put in gun safes to keep condensation from forming in the box but it doesn't put out enough heat. So as long as the temp in your hange is above freezing you will be OK.

Mike T

[lhendrick]

Originally Posted by MikeT

Greg, I built the same Velleman kit that you built and put the additional relay to handle the current of the heater and put it out at the hanger. It worked when I put it out there, but wouldn't work when needed. I did some research and one of the two IC's quits working at 32 degrees f. I see you live in NV. so you might be OK, but here in Michigan it doesn't work a good part of the winter. I also tried putting one of those heaters they put in gun safes to keep condensation from forming in the box but it doesn't put out enough heat. So as long as the temp in your hange is above freezing you will be OK.

Mike T

Perhaps some heat wrap tape like that used to keep pipes from freezing??

[Greg Arehart]

Mike,

Correct, the circuits quit working around freezing (I also found out by experience since I didn't read that in the instructions). I wired two christmas-type light bulbs into the circuit so that they are continuously on, and the heat from these has been sufficient to keep the board working fine down to at least 10 or 15-degree nights (I haven't checked on colder nights). The bulbs are inside the box and wrapped in Al foil to keep any light from disturbing the photo eye. I used two bulbs on the assumption that one would fail eventually and I would then still have at least one heat source. You could do similarly but use three or four bulbs, or that heat tape. Insulating the box would also help.

cheers,
greg

[bullojm1]

I purchased a device which takes a cell-phone SIM card and has relays built onto it to control my sump heater. It is great because I can send it a text message, and it will reply with an acknowledgment. And it works quite well in sub-freezing environments. A T-Mobile pre-paid SIM card costs about $10 every 3 months to keep it active.




Full Details are at: http://www.rvplane.com/?categoryid=10000&dayid=1005

Total cost was around $250