remote control
I am for the first year in electrical engineering so sorry for this question but i couldn't test it by my own.
One of my lecturers said that the remote control of a TV saves the channel we choose, and that when we press the "last channel" button, the remote sends the channel and not the "return" signal. Is this true?
Thank you all for your answers, they were all good ways to test it.
I will inform my instructor about them!
Usually the keys are multiplexed so you cannot easily use an output directly.
You could, however, emulate the key closures with an analog switch such as a 74HC4066 quad analog switch. The ground on the remote should be commoned with the controlling circuit. Power for the 4066 should be the same as the MCU I/O power.
You would send a pulse to the analog switch to emulate the key press- maybe 250ms.
Any common IR or RF Receiver, a microcontroller to parse the signals, and a H-Bridge Driver. An H-Bridge provides a electrical motor direction control, instead of mechanical direction control based on a DPDT switch.
Alternatively, a DPDT Relay could be used. An H-Bridge would be better, in terms of Size, Speed (for PWM or electronic speed control), and Power Consumption, but a relay would be simple enough for regular on/off direction control. A microcontroller would need a simple transistor/mosfet driving circuit to control the relay.
Best Answer
No. Absolutely not. The "Last/Return/Previous Channel" button is a unique function code that the TV interprets!
For the most common IR control protocols, Philips' RC5, Sony's SIRC or NEC, the remote is normally an application-specific integrated circuit (ASIC) with hardcoded TV codes for fixed remotes or a microcontroller with a reprogrammable eeprom for learning remotes (programmed via special codes or through a programming interface like JP1 or even IR learning).
The remotes have a single code programmed into each button, and that does not change without intentional reprogramming. These codes are arbitrary for the remote and depend on the TV to interpret. You can see an example for Insignia TVs here: http://www.getzweb.net/jp1/data_returns/DeviceEFCs.php?type=TV&devid=1204&webpid=++396
Each of these codes are single function, unless you get into more advance macros which are a group of codes assigned to the same button that get sent in order.
Unlike some of the dubious test methods listed above, you can actually decode the actual code sent by your remote. All you need is a common IR receiver module and a microcontroller (MSP430, Arduino) or computer like the Raspberry PI.
Once you do, you will find that the "Previous" button will always send the same exact code, regardless of what channel you have switched to and when. The remote does not actively track what channel or ANYTHING you do.
A different way would be to use a IR Learning Remote like the Harmony remotes. If the previous button was an active copy of the last channels selected, then you could not clone the feature.
Further note, the On/Off button is typically a single code that the TV interprets as toggling the current state, but discrete On and discrete Off codes often exist for any given tv, as well as dedicated "Input Source X" button instead of "Next Input" type codes.