# please let me know this circuit.

#### jack hammer

Joined Jan 25, 2016
3
Hellow.
this circuit is infared receiver circuit for toy car motor.
but i don't know function of r11,r12,C5 in this circuit.
please let me know why use these.

#### SLK001

Joined Nov 29, 2011
1,548
C5 is a filter capacitor. It stablizes the power for the IR phototransistor to minimize false triggering due to relay switching.
R11 is a bleeder resistor, which rapidly discharges C5 when power is off.
R12 is biasing resistor for phototransistor X1.

All this is just an educated guess.

#### R!f@@

Joined Apr 2, 2009
9,740
R11 & R12 forms a voltage divider to lower the 6V depending on the IR operating voltage. C5 is used to stabilize that voltage.

#### blocco a spirale

Joined Jun 18, 2008
1,546
R11 & R12 forms a voltage divider to lower the 6V depending on the IR operating voltage. C5 is used to stabilize that voltage.
R12 = 560Ω
R11 =100kΩ
Doesn't really work as an effective voltage divider.

I would say that R12 and C5 operate as a low pass filter to keep relay and motor noise away from the IR receiver.

#### R!f@@

Joined Apr 2, 2009
9,740
R12 = 560Ω
R11 =100kΩ
Doesn't really work as an effective voltage divider.

I would say that R12 and C5 operate as a low pass filter to keep relay and motor noise away from the IR receiver.
You may be correct.

I stand corrected, I believe.

Last edited:

#### blocco a spirale

Joined Jun 18, 2008
1,546
It happens, sometimes

#### Sonoran Desert Tortoise

Joined Oct 30, 2014
79
Hellow.
this circuit is infared receiver circuit for toy car motor.
but i don't know function of r11,r12,C5 in this circuit.
please let me know why use these.
View attachment 99399
R11 & R12 forms a voltage divider to lower the 6V depending on the IR operating voltage. C5 is used to stabilize that voltage.
R12 = 560Ω
R11 =100kΩ
Doesn't really work as an effective voltage divider.

I would say that R12 and C5 operate as a low pass filter to keep relay and motor noise away from the IR receiver.
C5 is like a battery that quickly drains. R12 makes sure the battery doesn't refill quickly. That way, the power to the sensor runs out (5mA output). Then it will shut off until C5 is recharged, then fire again. These little sensors become saturated and shutdown if given a constant pulse train of IR. This designer made the sensor immune to constant pulse trains. Shutdown/recharge/restart should be fairly fast. I have no idea what he was thinking on the 100k resistor other than some type of pull down resistor for the sensor while it is "powered down". The op will have to try with/without the resistor to see what is going on.

some newer 38k sensors are available that are immune to the constant pulse issue.

#### blocco a spirale

Joined Jun 18, 2008
1,546
C5 is like a battery that quickly drains. R12 makes sure the battery doesn't refill quickly. That way, the power to the sensor runs out (5mA output). Then it will shut off until C5 is recharged, then fire again. These little sensors become saturated and shutdown if given a constant pulse train of IR. This designer made the sensor immune to constant pulse trains. Shutdown/recharge/restart should be fairly fast. I have no idea what he was thinking on the 100k resistor other than some type of pull down resistor for the sensor while it is "powered down". The op will have to try with/without the resistor to see what is going on.

some newer 38k sensors are available that are immune to the constant pulse issue.
No, none of that is correct.

There is no "Shutdown/recharge/restart" cycling. Have you read the datasheet for the TSOP1738?

#### R!f@@

Joined Apr 2, 2009
9,740
C5 is like a battery that quickly drains. R12 makes sure the battery doesn't refill quickly. That way, the power to the sensor runs out (5mA output). Then it will shut off until C5 is recharged, then fire again. These little sensors become saturated and shutdown if given a constant pulse train of IR. This designer made the sensor immune to constant pulse trains. Shutdown/recharge/restart should be fairly fast. I have no idea what he was thinking on the 100k resistor other than some type of pull down resistor for the sensor while it is "powered down". The op will have to try with/without the resistor to see what is going on.
Wow!
Where did you learn that ?