For my project I need a powerful IR transmitter able to trigger IR home appliances. I have made a basic transmitter using a transistor, but the distance is very short so I came up with the below schematic based on what I could find on the internet.
I plan to use two different IR leds, and a IRLZ44, the power source would be a 5V (VBUS) while the GPIO driving this is 3.3V. Max allowed A from VBUS is not really clear, I found 500mA or 1A unfortunately the specification of the board I have are not clear (lolin s2 mini (maybe a clone)).
Can anyone validate the schematic below please to verify the correctness?
Kind regards,
dk
The circuit is fine, but it is not clear what you mean by VBUS. If you are powering the device from a USB port, look up and obey the maximum allowed current draw from the USB port.
You can always use a separate power supply for the LEDs, for example a 3.7V 18650 LiPo cell. Reduce the current limiting resistor values accordingly, and connect battery negative to MCU and MOSFET ground.
I appreciate the feedback.
VBUS is the label on the lolin s2 is the 5V pin looks like it is directly connected to the USB connector.
Yes it all will be power by the USB port.
What if I reduce the number of leds from 4 to 2? should I change anything else?
Kind regards,
dk
You are allowed to draw 500 mA from a port in USB 2.0, 900 mA in USB 3.0.
As suggested above, placing two IR LEDs in series with an accordingly reduced current limiting resistor, will reduce the total current draw by a factor of two.
If you use one LED of each type in the series connection, you can use the same resistor value.
MOSFETS generally have lower on resistance (voltage drop) than bipolar transistors, and do not require steady-state (base/gate) current to maintain the fully conductive state.
Oh, this I did not notice, I took idea from another schematic I found online with 3.3V drive. I see what you mean this is not specified for that and it might cause problems to the MCU
I m actually working on a PCB but I can do on TH soldering and would like to test this on breadboard... that's why I was looking for a TH mosfet.
The other alternative is to change to a transistor, which I have a few, but I was not really successful with the first design in terms of distance of signal. I will post it here to see if I can improve it
The other design alternative is the one below, but not sure if this is pushing at maximum the two LEDs. I had a similar design with only the VSLY5940 but the range is around 5 meters, not sure if I made a mistake.
The VSLY5940 has a very very narrow beam angle of only 3 degrees.
So the transmitter and receiver need to be perfectly aligned. If you are off just 3 degrees in any direction the amount of power seen by the receiver will be cut in half.
I was not able to measure, the input of the MCU is too fast for my multimeter to adapt.
I tried to put stable pin on but the transistor heated up super fast and I immediately disconnected it. Actually this is concerning, if for what ever reason the MCU freezes and the pin remains on, this might burn... was this caused by the collector current too high, or the base current (having the pin always on)?
not sure if I made the right calculation:
with the voltage of 5V, using a 19 Ohm resistance I should have 1.6V on both the LEDs with a current of 95mA. this twice maybe was too much for the transistor?
It might be the case that the 5V is a bit more like 5.2 and the resistor are not precise, leading to a bigger current?
and would like to test this on breadboard... that's why I was looking for a TH mosfet.
