Smoke Detector Design Explanation - Renesas RL78/I1D User Manual

DETECT-IT RL78/I1D detector boards kit
Note : The motion sensor board has a second/alternate PIR sensor connected to MCU internal operational amplifier
channels Ch2 and Ch3. However, these Ch2/Ch3 operational amplifiers are not currently activated by the
current Firmware revision, then the second PIR sensor will not draw current. (However there is an additional
current drain thru R67 and R93 of about 0.34uA @3.3V that could be eliminated by removing either of these
resistors).
A buzzer is used to give the alarm, it is managed by the MCU (transistor driver).
The push button is used for the reset function.
The board can be powered by a 3V lithium battery (CR123). It can also be powered by power supply (E1 power supply
or external power). One battery CR123 is provided into the kit for the 4 boards. The E1 debugger is not provided.
Caution: Battery should never be installed when using E1 power supply or external power supply via CN02/CN01.

Smoke detector design explanation

The Smoke detector is an infrared reflective smoke sensor type. It will alert when smoke (or simulated smoke) is
detected for 3 seconds.
In order to test the smoke detector board, you can use product like "smoke check" or "smoke in a can" brand spray in
order to simulated smoke. The board will work with real smoke as well. The board is designed to reject any ambient
infrared light from direct/indirect sunlight or man-made IR sources. For the smoke sensor, the integrated operational
amplifiers of the RL78/I1D are used to perform the current to voltage (trans-conductance) conversion needed to detect
IR photodiode avalanche (reverse bias) current when reflected IR light is present. Only 2 operational amplifiers are used
in the Smoke detector demonstrator, and they are operating in High Speed mode. The RL78/I1D comparators are not
used for this Smoke detector design.
The optical smoke chamber is the first element of the analog front end, this chamber is used to reduce the ambient light.
Inside an Infrared emitting LED and Infrared Photodiode are used to detect smoke particles by reflected IR light.
This optical smoke chamber is connected to 2 operational amplifiers of the RL78/I1D:
-
First stage (DC) trans-conductance (current to voltage) amplifier
- Second stage DC amplifier, to provided additional DC gain.
The on-chip comparators are not used in the Smoke sensor board.
A buzzer is used to give the alarm, it is managed by the MCU (transistor driver).
The push button is used for the reset function.
UM-YDETECT-IT-RL78 V1.30
Figure Smoke sensor block diagram
Kit User Manual
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