Posted: Sun Sep 14, 2008 10:18 am
No good... my wife hated the idea of not having lights at night upstairs... she was right, of course. It was really inconvenient to have to go downstairs to turn the power on so the inverter just got left on standby all the time.
I had a look around Maplins for a wireless relay. I'd used one before for an electric garage door at my previous apartment but they were really expensive (about 30 Pounds). It was a high security one with up to four learned remotes and code hopping - ideal for a garage door but overkill for a remote light switch.
Wandering around the supermarket today I noticed a mini wireless door bell kit. I've got one for our front door already but this one was smaller and had a LED that lit up when you pressed the button as well as making a noise. It had 64 key codes to cope with neighbours using the same transmitter and was only 10 Pounds. It's battery operated (a 12V sausage in the remote and 3x AA in the receiver). These things have come on in recent years. The one on my door takes 2x C batteries and seems to last about a year. Considering that the receiver is a radio, that's pretty impressively low power consumption.
Back at home, I took the new door bell receiver apart. I was lucky in that the LED comes on solidly while the digital chip is playing the sound. This made the thing ideal for switching the inverter remote on and off as it has a momentary press switch that toggles the inverter. It's a logic switch and shorting it with a test meter showed 12V at 3mA when working. I didn't want to use a relay in the receiver as it takes too much power and the thing only had 3x AA batteries. Curiously, only two are needed for the receiver, the third is in series but the 4.5V only goes to the music chip via the loudspeaker. I could take out the third battery and the LED still came on when you pressed the button (just no sound).
I figured that an opto-isolator would do the trick for providing another switch in parallel to the press button but didn't have one handy. What I did have was a LED in the receiver and a miniature photodiode salvaged from the position sender of a printing calculator print drum. So I cobbled the two together by cutting the curved top off of the LED to make it flat and superglued the photodiode on to it. As they were both water clear, it didn't work very well as stray daylight kept turning the photodiode on. So I encased the whole thing in some black shrink tubing and it worked a treat.
I stuck the bell button on the wall upstairs and it works just fine. There's a couple of seconds delay before the solar mains comes on as the inverter does some checks and winds itself up before enabling the output (so it can start big loads cleanly). In fact, it's made the upstairs lights better at night. Now when we go to bed we can leave the bathroom light on and turn off the solar mains with the remote. When one of us has to "go" in the night, we can turn on the bathroom light from the other end of the hall.
I'm happy as I can save the solar batteries at night. The wife is happy because she can turn on the bathroom light remotely and the cat is happy because she no longer gets stepped on in the dark while sleeping in the middle of the hall like some kind of rug.
I had a look around Maplins for a wireless relay. I'd used one before for an electric garage door at my previous apartment but they were really expensive (about 30 Pounds). It was a high security one with up to four learned remotes and code hopping - ideal for a garage door but overkill for a remote light switch.
Wandering around the supermarket today I noticed a mini wireless door bell kit. I've got one for our front door already but this one was smaller and had a LED that lit up when you pressed the button as well as making a noise. It had 64 key codes to cope with neighbours using the same transmitter and was only 10 Pounds. It's battery operated (a 12V sausage in the remote and 3x AA in the receiver). These things have come on in recent years. The one on my door takes 2x C batteries and seems to last about a year. Considering that the receiver is a radio, that's pretty impressively low power consumption.
Back at home, I took the new door bell receiver apart. I was lucky in that the LED comes on solidly while the digital chip is playing the sound. This made the thing ideal for switching the inverter remote on and off as it has a momentary press switch that toggles the inverter. It's a logic switch and shorting it with a test meter showed 12V at 3mA when working. I didn't want to use a relay in the receiver as it takes too much power and the thing only had 3x AA batteries. Curiously, only two are needed for the receiver, the third is in series but the 4.5V only goes to the music chip via the loudspeaker. I could take out the third battery and the LED still came on when you pressed the button (just no sound).
I figured that an opto-isolator would do the trick for providing another switch in parallel to the press button but didn't have one handy. What I did have was a LED in the receiver and a miniature photodiode salvaged from the position sender of a printing calculator print drum. So I cobbled the two together by cutting the curved top off of the LED to make it flat and superglued the photodiode on to it. As they were both water clear, it didn't work very well as stray daylight kept turning the photodiode on. So I encased the whole thing in some black shrink tubing and it worked a treat.
I stuck the bell button on the wall upstairs and it works just fine. There's a couple of seconds delay before the solar mains comes on as the inverter does some checks and winds itself up before enabling the output (so it can start big loads cleanly). In fact, it's made the upstairs lights better at night. Now when we go to bed we can leave the bathroom light on and turn off the solar mains with the remote. When one of us has to "go" in the night, we can turn on the bathroom light from the other end of the hall.
I'm happy as I can save the solar batteries at night. The wife is happy because she can turn on the bathroom light remotely and the cat is happy because she no longer gets stepped on in the dark while sleeping in the middle of the hall like some kind of rug.