Assembly Instructions

Here are complete step-by-step assembly instructions with an explanation of some optional items. At the end of the page there is a YouTube video that also demonstrates a complete start to finish assembly.

Standard Assembly

The NPN and PNP transistors used in this project look extremely identical. There are only very tiny part numbers written on them. We highly recommend you not take the parts out of the package until you are ready to use them. Similarly the TSOP and TSMP devices look identical and their part numbers are even smaller.

Begin by soldering in the three transistors. The NPN PN2222 goes in position T1. The silkscreen shows that flat side of all three transistors faces left. The 2 PNP PN2907 transistors go in positions T2 and T3.

Insert the 1K ohm resistor horizontally just below the left PNP transistor.

Insert the 2 LEDs making sure that the long anode wire goes on the right and the short cathode goes on the left. It doesn't matter whether the wide angle or narrow angle LED goes on the left or the right. You can put the LEDs in flush to the board but usually I prefer to have them stick out a little bit so that you can bend them forwards or backwards at any angle. See the image below.

Solder them all in place and clip leads on the backside.

Optional Components and Features

Now you have some decisions to make on various options for the board. Depending on your application needs you may or may not want to include current limiting resistors. There are also options for how to orient the receiver and learner devices. Finally, you have the option of providing a different supply voltage for the output LED portion of the circuit versus the input receiver portion of the circuit.

Current Limiting Resistors vs Jumpers

The first option is to add a 33 ohm current limiting resistor in line with each of the LEDs. Without them, this circuit will drive the IR LEDs beyond their rated continuous current capacity. However because IR signals are intermittent and modulated it is safe to do this. On the other hand your power supply has to be able to supply that much current. On some applications if you are drawing your power from an Arduino board powered by USB it may not be able to supply that much current and operate the board at the same time. For example we use this board in an Internet of things (IoT) IR remote based on an Arduino Yun which draws a lot of power for the embedded Linux processor and the Wi-Fi capability. The board could not power this IR device as well. Adding the 33 ohm resistors lowered the current requirements and made this project work.

Also, if your application is going to have lots of continuous use such as controlling an IR robot or drone, you might also want to consider using current limiting resistors. Such applications put more strain on the LEDs and the circuits than normal use as a TV remote.

On the other hand if you are powering the board from a battery source, such as we do in our assistive technology Ultimate Remote, the extra power that comes from leaving out the current limiting resistors is really useful.

So you have a choice of including the resistors in positions R2 and R3 or simply inserting a jumper wire instead. You could also install the resistors and put a jumper or solder bridge on the backside that could be soldered or unsoldered as you experiment.

When originally designing with this board, I wanted to make it as small as possible but I didn't want to use surface mount components, so I decided to stand these resistors on their end. See the image below on how to install them or watch the YouTube tutorial video at the bottom of this page.

Receiver Configuration

If you're only using the board for output purposes, you do not need either of the two receiver devices and you can skip their installation. If you are doing input you, will want to use a TSOP38238 from Adafruit or a TSOP38438 from DigiKey. The latter has slightly better automatic gain control circuitry built in, but either device will work well. This device reads an infrared signal modulated at 38 kHz and de-modulates it into a clean square wave so that a project can detect the patterns sent by an infrared transmitter such as a TV remote. Most consumer electronic devices use signals modulated at 38 kHz however some use 36 kHz, others 40 kHz and a very few use 56 or 57 kHz. Although this device is tuned to receive at 38 kHz, it will typically read 36 or 40 kHz signals quite well. Typically it cannot read higher frequency signals such as 56 or 57 kHz. You can purchase other types of TSOP devices that are specifically tuned to the frequency you are using but we feel that the 38 kHz variety provides a good compromise.

The TSOP device cannot tell you the frequency of the incoming signal. If you're using this device just to control something you don't really need to know the frequency. However if you are doing analysis of an unknown protocol, you might want to know the frequency information. This requires a different device called a TSMP58000. It does not de-modulate the signal, it just gives the raw information. IRLib2 has sample programs that show you how to read the frequency using the TSMP58000.

The PCB has space for both devices. The upper right corner is for the TSOP which is described as a "receiver" and the upper left is for the TSMP which is described as a "learner", because with the proper software, that device could be used to learn all of the information about a particular signal.

The board has been configured in such a way that you can aim either of these devices in any of 4 directions on either the front or the back of the board. When the lens of the device is facing you, pin 1 is on the left. As long as you insert that pin in one of these square pads, and place the other two pins in the adjacent round holes, the device will operate properly.

Supply Voltage Options

The sending portion of the circuit consisting of the LEDs and the driving transistors can be powered separately from the receiving portion consisting of the two receiver chips. Either portion of the circuit can be operated at 3.3v or 5v and in most circumstances, you will want to have them both powered at the same voltage. However, in some cases if you have 5v available to power the LED drivers but are using a 3.3v microcontroller such as an Adafruit Feather, you MUST supply the receiver chips with the same voltage as your processor. They will output a signal at whatever supply voltage you provide. So while it would be advantageous to have 5v on the LED drivers to give you a stronger output, you cannot attach 5v to the receivers and then connect them to a 3.3v board.

On the left side of the board there are 2 columns of supply pins. The column on the left is labeled "+3.3v" and it is the power supply for the TSOP and TSMP devices. The second column is labeled "+5v" and powers the transistors driving the LEDs. Both circuits share a common ground connection.

There are three options available.

  1. You are using a 3.3v controller and do not have 5v available to drive the LEDs so you will use 3.3v for both.
  2. You are using a 5v controller and will be using 5v for both parts of the circuit.
  3. You have a 3.3v controller but 5v is available separately to drive the LEDs.

For option 1 or 2 you should jumper together the 2 power buses and connect a single wire to either of those and supply the appropriate voltage. For option 3 you should leave the jumper out and supply 3.3v to the left terminal and 5v to the right terminal.

This image illustrates using separate power connectors for 3.3v and 5v. It also highlights areas where there are added additional power and ground connections you might find useful for connecting other components to this board.

This image shows how you would jumper together the two power buses when using the same voltage for both input and output portions of the circuit.

Pinout Information

We've also attached wires to the other pins. You could however solder in headers.

As we previously explained, each of the columns of pins on the left are connected to either the receiver chips or the LED driver circuit. On the lower right, the right-hand most 5 pins are all ground pins.

The pin left of the ground, which has a blue wire in this illustration, is called "Recv" and is the output from the TSOP device on the upper right portion of the board. This pin can typically be connected to any digital input pin on your Arduino, however, it is most useful when connected to a pin that can handle pin change interrupts.

To the left of that is a yellow wire marked LED. It drives both LEDs through the driver transistors. This pin has to connect to a PWM pin on your Arduino. There is information in IRLib instructions about which pins can be used for various popular boards.

To the left of that, there is a green wire connected to a pin label "Learn". It connects to the TSMP58000 in the upper left portion of the board. It can be connected to any digital input pin, but it must support pin change interrupts. Again, more details and be found in the IRLib documentation.

The YouTube video below will walk you through this entire construction project.

This guide was first published on Aug 25, 2019. It was last updated on Aug 25, 2019.
This page (Assembly Instructions) was last updated on Jul 14, 2020.