Picaxe Interface Options for use with the Parallax motion sensor
   
   
This section describes other circuit options that can be connected to a microcontroller. If you have not already done so see my page on controlling an MP3 player with a Microcontroller before reading this page. I use the Picaxe microcontroller which I think is the cheapest and easiest to use but you can use any microcontroller or controller (e.g. prop 1, etc) with these circuits.  By using one of the circuits below or the simple transistor switch which is used to control the MP3 player should be able to control just about any type of prop.
   
   
The circuit below is used to control an electromechanical relay. A relay can be used to switch both AC and DC voltages, close switch contacts such as a prop try me button or a fogger control switch, or any other prop or device that requires a switch closure to activate. NOTE: The Diode across the relay must be used it is there to protect the transistor. Current flowing through a relay coil creates a magnetic field which collapses suddenly when the current is switched off. The sudden collapse of the magnetic field induces a brief high voltage across the relay coil which is likely to damage transistors and ICs. The protection diode allows the induced voltage to drive a brief current through the coil (and diode) so the magnetic field dies away quickly rather than instantly. This prevents the induced voltage becoming high enough to cause damage to transistors and ICs. This circuit may also be used for a solenoid as well as a relay. By bringing the pin high will activate the relay or solenoid.




This circuit is used for a relay or solenoid whith a voltage other than 5 volts. Notice how the grounds (0V) are connected from the 2 different voltages. All grounds in electroncis must be connected together.





Motors can also be controlled just like relays. Motors being inductive devices also require the protective diode to protect the transistor or mosfet. You can use either a transistor or a mosfet to control a motor but a mosfet is better suited to the task due to almost no voltage drop across it thus allowing the full motor supply voltage to be applied to the motor. Make sure the mosfet or transistor that you use has enough current to handle the motor. As a rule of thumb the device should be able to handle a least twice the current ot the motor. A heat sink may be required on the mosfet or transistor for a high current motor. By bringing the pin high will turn the motor on.




The picaxe microcontroller can control servos directly. Some controllers can not control servos. Check your controller documentation to be sure. The servo can be controlled by the servo command. Please see the picaxe documentation for more information (see link above). Once the servo command is used the servo will hold that position until another servo command is used or power is removed. Note the connection in the lower left of the circuit is connected to the picaxe 5V ground (0V).





To control AC devices an electromechanical relay can be used but there is a better type of relay made from an electronic circuit and has no moving parts and does not require a protection diode. It is called a solid state relay or SSR for short. With this relay the AC is completely isolated from the control circuit so it can not damage the control circuit in case there is a problem. This is the preferred method of controlling AC devices. The relay is controlled by a simple 5 volt supply from the controller. The two circuits below show how to connect an SSR. In the first circuit everything in the dotted box is the SSR contained in one package. The relay is switched on with a low (0v) on the control pin. In the second circuit the relay is switch on by a high (5V) on the control pin. Either circuit will work it depends on your preference. The AC load indicated in the circuits can be a spot light, a pnuematic valve, an AC motor, or any other AC device as long as it does exceed the current ability of the SSR. Solid state relays come in almost any current configuration.