This posting covers the first part of the electrical wiring for the Sofa-bed.
WARNING: Messing with electricity can be dangerous. If handled unwisely it can cause fire, death and general mayhem. If you don't know what you are doing, hire someone who does.
I'm not an electrician and have had no formal training on the subject so don't believe a word of what I say. You have been warned.
The sofa-bed's conversion from sofa to bed is accomplished with the mechanical force provided by two different actuators. The Drive Actuator causes the Seat Platform to move forward or backward. The Lift Actuator raises and lowers the Back Platform.
The actuators are powered from a 12 volt battery (or in my case two 6 volt batteries). There are two wires running to the actuator motor. To get the actuator to change direction you simply have to reverse the polarity of the two wires. That means if one wire was hooked to the positive battery terminal move it to the negative terminal and vice-a-verse with the other wire.
If you watch the
in operation you might have noticed the two actuators operating at different times. This is accomplished with limit switches. A limit switch is activated when something presses against it as opposed to a wall switch which you "flip".
Here is a picture of one of the limit switches I'll be using. Notice the small lever with the roller on the top of the switch. The movement of this lever is what causes the switch to open or close.
On the left side of the switch you will see two tabs. The tabs are marked "NC" and "NO". The markings mean "Normally Closed" and "Normally Open".
What that means is if the switch is in the "open" position, which it is in the photos, there is a current path from the "Com" tab on the right of the switch to the "NC" tab. When the lever is depressed the switch is considered "closed" then the current path transfers to the "NO" tab.
Along with the limit switches I'll need a couple of diodes to control the actuators. A very simple description of a diode is that it's a electrical component that only allows current to flow in one direction. Here is a picture of one of the diodes I'll be using.
Notice the silver band around one end of the diode. The band denotes the cathode end of the diode. It helps me remember how a diode works by thinking of it's electrical symbol.
If you think of current as flowing from positive to negative you can see how the triangular shape is pointing in the direction of current flow. While the vertical line resembles a check valve that swings down to prevent the flow of current in the opposite direction. Anyone who really knows about electronics will surely tell you there are different kinds of diodes and it's more complicated than I've explained but hey, this works for me.
"I am serious ... and don't call me Shirley." Happy 30th Birthday to "Airplane!"
One more electrical part before I can start putting it all together. From Radio Shack I bought this toggle switch. It's a 3 position (ON-OFF-ON) DPDT (Double Pole - Double Throw ) switch.
The metal face-plate shows it's 3 position. The six wire connectors on the back indicates it's DPDT. I'll use this switch to reverse the polarity of the electrical connection to the actuators.
This shows how I hooked up the switch to the batteries and to the actuators.
One small note. I forgot to add a fuse to the circuit drawing which strangely enough matches what I did in real life.