cwaitang26
New Member
Hi,
Active IR detectors detect method by transmitting IR pulse sequence and confirm detection only when Rx receive back correct sequence of Tx IR pulse reflected back from object.
Conventional design use signal conditioning such as filters and pre-amps to properly condition Rx signal before comparing to preset threshold level. Det is confirmed ONLY when threshold level of Rx signal (after condition) AND Rx pulse sequence is correct within det window.
Suppose IR Tx freq is set to 3 - 20Hz (max) with pulse width of 200 - 300us(fixed by design/functionality constraints), quite impossible to filter out low freq PD/PT noise, consider new detect method described.
Active infrared detection and conversion circuit includes a photodiode/phototransistor, a current amplifier, a capacitor, and a signal processor circuit (MCU).
Upon power up, MCU send signal to charge up cap to preset HIGH voltage lvl before turn on IR Tx.
When IR PD/PT is exposed to incident infrared, it generates a transient current, this incident current (>dark current) is amped by current amp and used to turn on transistor sw (darlington pair) to discharge cap. This discharge timing is < dark current discharge timing of cap (RC ckt used for discharge if trans sw not turn on).
Cap discharge cycle is fed to hysterysis ckt to wake up MCU when Vc fall below LOW threshold. MCU then compare the cap discharge time with a long-term cap discharge time under dark current. MCU then charge up cap to preset HIGH lvl to wait for next discharge cycle. Suppose each cycle of cap charge/discharge timing has taken the signal pulse width and frequency of Tx pulse seq into consideration.
MCU confirm det only when NUMBER of faster cap discharge cycles equal to number of Tx IR pulse.
MCU may further calculate and update long-term average cap discharge time based on dark current to filter out unwanted background IR noise and component tolerance variations.
Would this method work practically? Any unforseen problems?
Next, would this method able to compensate for both temp drift and aging of electronic components (Photodiode & Cap etc)?
Active IR detectors detect method by transmitting IR pulse sequence and confirm detection only when Rx receive back correct sequence of Tx IR pulse reflected back from object.
Conventional design use signal conditioning such as filters and pre-amps to properly condition Rx signal before comparing to preset threshold level. Det is confirmed ONLY when threshold level of Rx signal (after condition) AND Rx pulse sequence is correct within det window.
Suppose IR Tx freq is set to 3 - 20Hz (max) with pulse width of 200 - 300us(fixed by design/functionality constraints), quite impossible to filter out low freq PD/PT noise, consider new detect method described.
Active infrared detection and conversion circuit includes a photodiode/phototransistor, a current amplifier, a capacitor, and a signal processor circuit (MCU).
Upon power up, MCU send signal to charge up cap to preset HIGH voltage lvl before turn on IR Tx.
When IR PD/PT is exposed to incident infrared, it generates a transient current, this incident current (>dark current) is amped by current amp and used to turn on transistor sw (darlington pair) to discharge cap. This discharge timing is < dark current discharge timing of cap (RC ckt used for discharge if trans sw not turn on).
Cap discharge cycle is fed to hysterysis ckt to wake up MCU when Vc fall below LOW threshold. MCU then compare the cap discharge time with a long-term cap discharge time under dark current. MCU then charge up cap to preset HIGH lvl to wait for next discharge cycle. Suppose each cycle of cap charge/discharge timing has taken the signal pulse width and frequency of Tx pulse seq into consideration.
MCU confirm det only when NUMBER of faster cap discharge cycles equal to number of Tx IR pulse.
MCU may further calculate and update long-term average cap discharge time based on dark current to filter out unwanted background IR noise and component tolerance variations.
Would this method work practically? Any unforseen problems?
Next, would this method able to compensate for both temp drift and aging of electronic components (Photodiode & Cap etc)?
