The infrared emitter can be used as a control device for the infrared receiver.
It works with two batteries of 1.5 V or a 3 V lithium button cell type.
For the transistor to have enough gain at low supply voltage, is used a Darlington transistor.
Each network lag cells, R1-R2-C1-C2-C3-R3, has about the same time constant. Because cells do not influence each other in an undesirable, R2 = R3 = 3.8-3.8-R1 and R2. Because of this mutual influence, amplifier gain is slightly larger than the theoretical value of 18 dB.
Due to low voltage, LED diodes can not connect in series, and thus independently controlled by its own series resistor, R7 and R8.
The transmitter is switched on or off by connecting or disconnecting the supply voltage S1 ..
Current consumption depends on circuit voltage and as long the S1 button is pressed. When Ub = 2 V, the frequency is 29.3 kHz, peak current through the LED is 25 mA, and total current consumption is 27 mA. When Ub = 3.2 V, frequency is 30.4 kHz, peak current through each LED is 64 mA, and the total current consumption is 63 mA.