IR Tester With SMD Components

Some time ago I had the opportunity to repair a larger number of IR (infra red) remote controls, different models.At that time I felt the need to have a device that would indicate the simple fact that a remote control emits an IR beam or not.

I wanted the device to be portable, which implies the presence of a battery for power supply.

I designed a scheme that allows very low consumption, which allows a long use of the battery, even in the absence of a power supply voltage switch, which we usually leave in the "ON" position.

Such a device, miniaturized, is presented below.

All electronic components are in current production and can be ordered from websites specialized in the sale of electronic components.

The PCB can be made at the factory or made by yourself, as shown in Step3.

In the conditions that the BPW41 type IR optical transducer does not receive an IR beam, the static operating points of the circuit are calculated in such a way that D1, D2 and all transistors Q1...Q5 are blocked. This means a very low current consumption from the source power supply (approx. 30uA at 12V), which allows a long battery life, even in the conditions where there is no a power supply voltage switch.

When diode D1 (BPW41) receives an IR beam, voltage pulses of tens...hundreds of microvolts appear at its terminals.This depends on the intensity of the IR beam and the distance from which it comes.

Because the blocking point of the transistors is chosen to be very close to their normal active region, the appearance of voltage pulses causes the transistors Q1, Q2 to work as amplifiers in common emitter connection.

From an alternating current point of view, the emitter of Q1 is grounded through C1.

Q1 and Q2 form an amplifier with high amplification, several thousand.

Q3 works as a common collector amplifier, in its emitter having (when there is an IR beam) pulses with an amplitude of 12V. These pulses discharge C2 when Q2 is saturated, so that when Q2 is blocked again C2 will charge through R8.The phenomenon repeats with a frequency that depends on the C2XR8 time constant.

Q4 is a common collector amplifier and Q5 a common emitter amplifier.

In the collector of Q5 is the buzzer Bz1 in parallel with D3. The current through the LED D3 is limited by R12.

Thus, upon the appearance of an IR beam, Bz1 will sound and D3 will light up in a rhythm given by the time constant R8XC2. See IR Tester.avi.

Now the battery consumption increases to tens of mA, but the test time is short and thus the battery life does not decrease significantly.

Electronic components:

Q1   BC847   Package_TO_SOT_SMD:SOT-23

Q2   BC857   Package_TO_SOT_SMD:SOT-23

Q3   BC847   Package_TO_SOT_SMD:SOT-23

Q4   BC847   Package_TO_SOT_SMD:SOT-23

Q5   BC847   Package_TO_SOT_SMD:SOT-23

R4   10K   Resistor_SMD:R_0805_2012Metric_Pad1.15x1.40mm_HandSolder

R3 1M Resistor_SMD:R_0805_2012Metric_Pad1.15x1.40mm_HandSolder

R2 50K Resistor_SMD:R_0805_2012Metric_Pad1.15x1.40mm_HandSolder

R5 47K Resistor_SMD:R_0805_2012Metric_Pad1.15x1.40mm_HandSolder

R8 100K Resistor_SMD:R_0805_2012Metric_Pad1.15x1.40mm_HandSolder

R6 10K Resistor_SMD:R_0805_2012Metric_Pad1.15x1.40mm_HandSolder

R9 10K Resistor_SMD:R_0805_2012Metric_Pad1.15x1.40mm_HandSolder

R12 1K Resistor_SMD:R_0805_2012Metric_Pad1.15x1.40mm_HandSolder

R10 10K Resistor_SMD:R_0805_2012Metric_Pad1.15x1.40mm_HandSolder

R7 10K Resistor_SMD:R_0805_2012Metric_Pad1.15x1.40mm_HandSolder

R11 10K Resistor_SMD:R_0805_2012Metric_Pad1.15x1.40mm_HandSolder

C3 33uF/16V Capacitor_SMD:CP_Elec_6.3x5.8

C1 2,2uF/16V Capacitor_SMD:CP_Elec_4x5.8

D1 BPW41N OptoDevice:Osram_BPW82 D2 1N4148W Diode_SMD:D_SOD-123

C2 0,1uF Capacitor_SMD:C_0805_2012Metric_Pad1.15x1.40mm_HandSolder

D3 LED LED_SMD:LED_1206_3216Metric_Pad1.42x1.75mm_HandSolder

BZ1 Buzzer-12V Buzzer_Beeper:Buzzer_12x9.5RM7.6

BT1 12V typ A23 Battery:BatteryHolder_MPD_BH-A23

R1 100K Resistor_SMD:R_0805_2012Metric_Pad1.15x1.40mm_HandSolder

PCB done as in Step3.

In Photo 1 you can see these components and in addition substances used for soldering with tin:

RF800 and the solution of rosin dissolved in thinner.

The fludor used is 0.7 mm. diameter.

Photo 1.1 shows a very useful IR Tester when working with SMD components.It can measure voltages up to 20V, resistors, capacitors, diodes. It can also be used successfully for measuring Zenner diodes and SMD LEDs. Any equivalent tester model can be used.

Photo 1.2 shows the thermostatic soldering station I used, model T12. Also here you can see the 0.7 mm fludor used. 60%Sn 40%Pb and the device to clean the tip of the letcon of oxides.

Photo 1.3 shows the soldering iron used at the soldering station, delivered with it and specialized in soldering SMD components.

Photo 1.4 shows a small workbench for SMD assembly.

At the base there is a small metal support on which we will do the manual assembly of the SMD(it is recovered from a disassembled LEDTV, it was part of the panel).

In addition to those presented previously, here are also:

-precision tweezers.

-electronic microscope 64X...32X.

-3X...5X magnifying glass.

-2 trays for SMD components, under which there are magnets, thus creating magnetic areas, very useful in order not to lose these components.

-digital mutimeter (any type).

In Photo 1.5 you can see: thinner and a medium-sized brush, the hair of which has been cut to approx. 2 cm. These will be used in the PCB "washing" operation, as will be seen in Step4.

At address:

https://oshwlab.com/TedyS/tester-ir-smd-1

the project is found: schematic diagram, BOM, PCB.

In our case, since it is a device made in the SMD technique, it is desirable to order the PCB from the factory, something that can be done easily and at a reasonable price directly from this address.

This is what I did too, the PCBs can be seen in Photo1, 2, 2.1.

For those who wish, there is also the possibility to make the PCB on their own by accessing the link:

https://drive.google.com/drive/folders/1ScImJ1335lxiO3EpnZqZ057iGkDFK8Mp?usp=share_link

Here is the entire project made in the KiCad version, a program that allows PCB printing and therefore its realization by the photo or PnP method.

A very good tutorial for soldering SMD components on PCB can be found at:

https://www.youtube.com/watch?v=fYInlAmPnGo

Here we present two methods of soldering and desoldering SMD components with tin.

Any of these methods is OK, everyone will apply the most suitable path for him.

Personally, this time I tried a slightly different method, using the solution of rosin dissolved in thinner (see Photo1), a soldering iron and 0.7mm fludor.

We will cover the PCB with a layer of rosin dissolved in thinner.

The PCB will be in a horizontal position and in this position we will place the SMD components according to the project or Photos 2, 2.1. In 10-15 minutes layer of rosin dissolved in thinner it will dry and the SMD components will adhere to the PCB, as seen in the Photo3.1.

Returning with the PCB in a horizontal position, we will solder the SMD components one by one.

For this we will use one of the precision tweezers, with which we will press the SMD component that will be soldered with 0.7 mm flux. and T12 soldering station.

Next we will "wash" the board.Using the thinner and the brush from Photo 1.5, we will cover the board with a layer of thinner, then following an energetic "brushing" in all directions. This will remove oxides and other impurities from the board, giving it a pleasant appearance and removing the possibility of unwanted contacts. The result can be seen in Photo 3.2.

Next, the 2 SMD capacitors and all THT components will be soldered with tin.

The board will also be "washed" on the back.

Done correctly, the assembly will work from the beginning, without problems.

If this does not happen, the most common cause is the lack of one or more tin solders.

These will be checked as well as an incorrect location or inappropriate value of the electronic components.

Finally, a sheet of non-conductive material will be cut to the size of the PCB. A few pieces of double-sided adeshive tape will be stuck on it, as in the Photo 3.4.

The foil will be attached to the board on the back, as in Photo 3.5.

Thus, there will no be the possibility of touching the tracks on the back of the PCB with conductive surfaces.

With this device, the distance from which the existence of an IR beam can be tested is usually from 2cm. at 1m.

Under normal use, the A23's battery life is a few weeks.

If we want to change the battery less often, we can use a trick based on the fact that the device works very well even at 9V.

For this we will solder on the back of the PCB an adapter for a 9V battery, type 6F22. Also here we will stick a double-adhesive tape, 3mm thick, as in the Photo 4.1

Then we will stick the 6F22 battery on the double-adhesive tape , as in Photo 4.2.

Now the device looks like in Photo 4.3 and will be able to be used without problems for several years, depending on the quality of the battery.

And that's it!