The Electronic Switch By James Goss     Mechanical switches have been around for many years and are still widely used in our hobby. They are relatively inexpensive and in most cases do an excellent job of switching the various things on our planes on and off. The basic four-channel plane will have a single switch to connect the flight battery to the receiver when it is time to fly. This switch is normally a double pole double throw switch that connects the battery for flight when it is on and connects the battery to the charge line when it is off. Even though you can now get an electronic switch for this task, I think I will stick to the mechanical switch for this task because of the simplicity.      Other than the main on-off switch, you may also need to switch other loads in your plane on and off. These auxiliary loads may be bomb drops, running lights, strobe lights, retracts, sound systems, smoke systems, ignition kill switches, and glow drivers to list a few. Using a mechanical switch for these loads means that you must have another servo that is devoted for this task. Most standard servos will weigh between 2.5 and 3.5 ounces and takes up about six cubic inches of fuselage space when mounted. Electric switches weigh less than one ounce and take up much less space. They do not require a servo; they simply plug into the receiver channel of your choice for activation.        When you look at the price for an electronic switch, remember to deduct the price of a servo because one is not needed. I am sure that everyone knows the theory of operation for a mechanical switch so I will not discuss that here. What you may not be aware of is that a mechanical switch will create some voltage drop when its contacts are closed and the load is connected. This is due to the contact resistance and the amount of voltage drop depends on how much current is flowing at any given time. So a switch of this type is not perfect, we have a tiny power loss across the switch. The electronic switch also has a voltage drop and is around .1 volt or less, if the power device is a Power MOSFET. If the power device is a transistor, it will drop a much higher voltage, about 1-volt.      All electronic switches that I know of today will use the Power MOSFET because of their high current capability. These tiny devices can handle several hundred amps with the most common ones being rated at 60 amps and 50 volts. A rating of 60 amps will handle anything on your plane that you can imagine. To connect the electronic switch you first must connect the load to the switch. Most manufacturers will have you do this by soldering the switch to the positive or negative side of the load. You can switch either one, it doesn't matter. As an example, you may connect the negative wire straight from the battery to the load and take the positive lead from the battery through the electronic switch and then to the load. To most electricians this arrangement would be called a switch leg.  Next, connect the e-switch to the receiver channel you want to control it. At this time you can check everything out for proper operation and adjust the turn-on sensitivity by adjusting a small pot if needed. If the switch is working backwards from the way you would like it to, you can move a Burg jumper that is located on the small board and it will reverse the on to an off state or the off to an on state. That's all there is to it! Wrap the e-switch in foam and you are ready to go. If you were using a servo to control a mechanical switch such as a limit switch (micro switch), it is sometimes challenging to accomplish this task. Coupling the energy from the servo to the switch is what I am talking about here. So the e-switch is much faster to install than the mechanical switch. Another really neat thing about these e-switches is the fact that they are optically isolated. This means that light is used to transmit the signal that turns on the MOSFET, not copper wire. The light will not transfer any noise that the load may generate back to the receiver causing a glitch. Let's see a mechanical switch do that!      An optical isolator is a small chip that has a light emitting diode inside that furnishes a light signal, either visible or infrared, when an input is present. The light is received by a small phototransistor, or other similar devices that are also inside the chip. This provides an output from the chip, either a high or low that represents the input signal. I will have an article on my web site that gives you more information on electrical noise in the future. By having optical isolation, your system will be free from any impure signal and operate smoother. The e-switch also has a much faster response time than does the mechanical switch. When contacts in a switch close or open, it takes time for the contacts to move, this is known as transit time. Electronics can operate almost at the speed of light. Of course the speed advantage may not be needed in some of our switching projects for our planes.     They are priced at around $49.00, but remember no servo is needed. Ram makes a nice one, but the Jomar (EMS) brand looks better. It comes with the plug of your choice already installed for the receiver. I use the Jomar e-switch for an ignition kill switch on my giant scale extra 300. It replaces the mechanical switch that was giving me trouble with contact bounce and allowing the engine to cut out during flight due to vibrations. There is quite a few components in use to make an e-switch and as you already know, the more components in use, the greater the chance of something going wrong. Other than contact bounce and noise pickup, the old mechanical switch is quite reliable. This same e-switch can also be used as your glow plug driver, especially if you have your engine mounted upside down. Mounting it this way makes it easy for the engine to flood. Each time you reduce your throttle the glow plug element cools off and the engine may shut down. If a glow driver is being used, each time you throttle back, the e-switch will energize the plug's element and keeps it hot for a nice low idle.      Here is another train of thought for you. A mechanical switch has very few parts for its operation and this is good. The bad thing is that they are mechanical parts that require physical movement to operate. Components that require physical movement have a shorter life that those that do not. The manufacturer can predict how long a component that has moving parts will last. As an example, the manufacture of a small relay may state that the device is rated for 500,000 operations before failure may be expected in the contacts. The electronic switch (e-switch) is a static device with no moving parts. You can't predict the life of a solid state device such as this. If not treated in some undesired fashion that tends to overheat it, the solid state device should last forever (however long that is). There is absolutely nothing to wear out like there is with a mechanical switch. Also, the servo that is required to actuate the mechanical switch has many more electronic parts than does the e-switch. So if increased parts means a more likelihood of failure, then the e-switch is better suited for the job. Looking at it this way, by using the e-switch you are not really adding more components as you might think, you are reducing them. Knowing this, I feel comfortable using this type of switch for all my auxiliary channels instead of a mechanical switch.      I thought you might enjoy seeing the schematic for a typical electronic switch. Notice the LED that indicates when the device is switched on or off. If you would like to see a detailed explanation of how this circuit works, it will be posted on my web site soon.