Co Detector Design Explanation - Renesas RL78/I1D User Manual

DETECT-IT RL78/I1D detector boards kit
The microphone is the first element of the analog front end. The microphone is used as the sensor for glass break event.
The microphone used is an Electret with frequency response from 25Hz to 16kHz.
The microphone is AC coupled to both a low pass and high pass sections, so that microphone output DC bias variations
does not affect the operational amplifier filter bias points:
• 2-stage low pass filter uses 2 channels (Ch0 and Ch1) of RL78/I1D internal operational amplifiers in low power
mode at about 4.5µA typical current drain total.
 The first stage has a nominal gain of 31 and a roll-off/cut-off frequency @ 34Hz.
 The second stage has a nominal gain of 26 at roll-off/cut-off frequency @ 154Hz.
 Therefore in both cases, GBWP (gain x frequency product) used on each stage is less that the operational
amplifier GBW = 40 kHz rating in low power mode. Since the operational amplifiers have a low current drain in
low power mode, they can be left on constantly to monitor a loud transient sound event.
• 2-stage high pass filter uses 2 channels (Ch2 and Ch3) of RL78/I1D internal operational amplifiers in high speed
mode at about 262µA total for both channels typical current drain.
 The first stage has a nominal gain of 20 and upper roll-off/cut-off frequency @ 24kHz.
 The second stage has a nominal gain of 5 and upper roll-off/cut-off frequency @ 1447Hz.
 Therefore in both cases, the GBWP (gain x frequency product) used is less that the operational amplifier GBW =
1.7 MHz rating in high speed mode. Since the operational amplifiers have a higher current drain (>100µA per
channel) in high speed mode, they are only turned on intermittently when analyzing a loud sound transient event.
So in glass break detector demonstration, the 4 operational amplifiers are used.
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.

CO detector design explanation

The carbon monoxide detector is designed to alarm when the concentration of CO gas is measured at a preset level of
100ppm. A higher threshold level can be set in software if desired.
UM-YDETECT-IT-RL78 V1.30
Figure Glass Break sensor block diagram
Kit User Manual
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