Practice without theory is blind, theory without practice is useless. Edison.
   Inicio      Projects

Remote control projects

The feeling that gives us to control any device wirelessly is almost magical. This can be achieved via RF, IR or ultrasound. In this case we will talk about the RF control.
Very high frequencies are used, which makes it impractical to create our own designs, because the circuits are very unstable and will not have the proper equipment to measure.
The simplest way is to use a commercial remote control module.
For small distances up to 100m we have several alternatives:
1.   To use couple module: RF transmitter and receiver, to which we must add an encoder and decoder integrated circuit respectively.
There are some transmitters and receivers RF modules assembled in a little board with one line pin format, suitable to insert into a main board, on which we can have the encoder or decoder. The last are those that prevent any similar RF frequency signal to activate the load on the receiver and activate only with a single code, which sends the transmitter. It's like a key.
The most popular encoders and decoders IC´s are the Motorola MC145026 and MC145027.
The Taiwanese Holtek has HT12X, the last letter indicates whether it is an encoder, decoder, the number of addresses, data and the application: RF or infrared (IR). These serve the same function as Motorola CI, but not a direct replacement.

2.   Using a transmitter with encoder included wich have its respective pair of receiver board. There are with one or more channels.

The FC-454-433-C04 model is composed of a "hand" transmitter, such as car alarms and a 4 channel receiver board with 4 SPDT relays. (See image above).
The transmitter uses a 23A 12V battery (similar shape as normal 1,5V battery) and is included, while the receiver board is designed to run on 12V. The transistor shaped integrated circuit in the upper left is a 5V fixed voltage regulator. Therefore finally the circuit runs with 5V, except for the relays.
For a different application where is not desired to use the relays, they can be replaced by a resistor to activate somewhat with the voltage drop across it. The relays are controlled by four transistors that are surface-mounted below the board. You will also see four free wheeling diodes for relay coils.
The 18-pin DIP format integrated circuit is the decoder, the PT2272L. Is not in the local market, but at least is commercial and their technical data sheets are available on the web. This information is very useful for projects, as we could for example change the code of several transmitters to match with a single receiver, so that several cars are able to open a single gate. Or, conversely, a single transmitter and multiple receivers, to trigger the gate house and the office with the same transmitter.
View decoder datasheets:

 Datasheet PT2272 

See remote control transmitter and receiver datasheets:

      Datasheet FC454remote  

For longer distances we only have the alternative of using aeromodelling transmitter and receiver, which have a higher price.


ON/OFF temperature control.

The ON / OFF controller is named because the fact that all the available voltage is applied to the load when it has no reached the desired temperature (reference) and zero voltage after reaching it. When you remove the voltage to the load, it gets cool causing voltage is applied again, and so on.
The controller switching device (contactor, relay, TRIAC, etc.) are constantly turn on and off.
To get information about the temperature the controllers use a sensor. In this case we use the LM335, which provides a voltage proportional to the temperature to which it is exposed.
This project was designed to maintain a 70 degrees Celsius temperature in a drying oven for photosensitive varnish for printed circuit boards manufacturing.

Headphones amplifier.

Although operational amplifiers, widely used in audio, have a low output impedance, they can not directly handle such low impedance loads as a 8 Ohm speaker or a headphones speaker of 32 Ohm nominal impedance.
The most common technique is to reinforce the operational amplifiers with transistors. Sometimes it may be hard to bias the transistors with a small current to prevent crossover distortion, because the two transistors used in complementary configuration will not have identical features.
Another alternative, simpler, is to implement a small amplifier with IC, as LM386N1.