|Revision 12 dated 02 Mar 2003|
Caveat: The information given below is intended to inform and in no way infringes upon any trademark rights owned by Michele Schieppati.
Michele Schieppati of Milano, Italy has developed a very useful switch that can be controlled from any channel on the typical Futaba® or JR® radio set up. The switch was designed to trigger the shutter on digital cameras without the encumbrance of a servo glued onto the camera.
However, apart from aerial photography, one of the more interesting features is that it can be used to trigger external loads that draw power either from the receiver battery or another external power source. Of further interest, the switch can be programmed to trigger at a preset interval of time, such as every ten seconds. Equally, the really interesting function is that the output signal can be set up to trigger at a preset interval of time and/or on command from the transmitter. Finally, the output signal can be programmed to be either a short pulse or a continuous ON command. That is flexibility!
The power consumption of the switch is 0.8mA when the Light Emitting Diode (LED) is OFF and 6.5mA when the LED is ON, so there is no risk of discharging the battery with the switch.
|Michele's switch is about as small and as light as you can possibly
imagine. In the image, the three wire lead (black, red and white) goes
to any spare channel on the receiver. The switch draws power from the receiver
battery and gets the command signal on the white wire.
The red and black lead on the left goes to the camera or external load. This lead has a very small male/female socket to allow quick disconnect.
The coin on the left side is a US cent to give some idea of the size.
The small red square red on the left is a programming jumper, while
the white square is an LED that lights in red or green to indicate programming
Shown below is a simple demonstration of controlling an EXTERNAL object using an EXTERNAL power source. The word EXTERNAL means that the object and the power source are not part of the receiver set up.
In the left frame the Schieppati Switch is programmed, is receiving
its power from the receiver battery and waiting for a command from the
transmitter via the receiver. In the right frame, an ON command has
been transmitted, processed by the receiver and interpreted by the Schieppati
Switch. The switch can handle up to 36 volts DC and 0.8 amps when
used in the simplest configuration as shown below. Higher loads can
be controlled as described later.
This application could be used to control any low power, non inductive resource such as an airborne sound module.
||If you want to control something using a coil operated switch, such
as one readily available at Radio Shack®, then certain precautions
must be taken. A coil is an inductive load, and under certain conditions,
back EMF can develop. Back EMF is "bad" and can blow the switch.
To protect the switch, a diode must be used. Diodes let the current
flow in only one direction, positive to negative and thus prevent the "bad
It is better to install a diode in parallel to the inductive load (i.e. coil) with the cathode connected to power supply + and the anode on the other end of the coil switched to ground. This will recirculate the extra reverse current generated by the coil when the circuit is opened.
One really safe way to protect the switch, and everything dangling from it, is to isolate the switch optically using a small optocoupler chip such as a TIL 111 - photo transistor. The signal from the Schieppati Switch would simply turn on a photo transistor within the chip which then allows a totally isolated circuit on the other side of the chip to operate. In essence, there is no electrical connection between the Schieppati Switch and the EXTERNAL load.
Airborne Glow Driver Circuit
||Michele has provided this generalized circuit that could be used
to switch two airborne glow plug drivers.
Q? is a P Channel MOSFET. R? is the value of the resistors, which are acting as voltage dividers, to drop the voltage to the specifications of Q?
The two devices are shown in parallel to increase the current draw required to drive two glow plugs. If only one plug is being driven, then eliminate one MOSFET and its attendant two resistors.
For this application, the Schieppati Switch would be programmed to switch ON below about 1/3 throttle and give a continuous ON signal to the glow driver.
When the receiver is turned OFF, the switch and glow driver would automatically switch OFF.
When your favourite plane crashes into tall grass, thick forest or a field of corn, it would be nice to be able to detect some sound coming from the plane. A very simple circuit to generate noise can be constructed that is simple, inexpensive, runs off the receiver battery and can be commanded by the Schieppati Switch. Simply use a "Y" harness plugged into any unused channel. Plug the noise generator into one branch (it will pick up only the red and black power source) and plug the Schieppati Switch into the other branch (it will take its power from the receiver battery and also receive the command signal on the white wire).
When the plane crashes, walk to the approximate crash site and give
the noise command using your transmitter.
The circuit shown can be very loud - as loud, if not louder, than a smoke detector/alarm. On the right, the components are shown mocked up on a "breadboard". The key component is the LM386 power amplifier. Soldered together, the electronics would be about one square inch and would weigh practically nothing - the speaker would be the heaviest component. If you do not want to build the circuit, simply go to Radio Shack® and buy a buzzer to match the nominal 4.8 volts from the receiver pack.
With the ultra light receiver packs available for park flyers, the GSmart Mini 3 digital camera, and the Schieppati Switch, what could be easier than taking photos from a small kite?
It is difficult to get good close-up shots of wildlife. A "blind" could be set up close to a feeding station. After several days, the animal/bird should become acclimated to the presence of the artificial object and pay it no heed. The Schieppati Switch, rigged to a typical receiver/camera outfit and installed in the blind, would permit the operator to trigger the camera from a distance. Since there is no camera noise or servo noise, the silent operation would not startle the target.
The Schieppati Switch would appear to offer many possibilities for
either static track-side or rolling applications. The switch is so small,
that combined with the new micro receivers, the complete assembly could
easily be hidden in an HO gauge box car.