So I'm trying to make a pulse sensor using TCRT5000 IR sensor and arduino UNO (giving out 4.8V really from 5V pin) (Baud Rate 19200), and I'm supposed to get a pulse plot like this

Ideal pulse curve

But I'm getting it like this curves attained

As you can see, absolutely no pulse is noticeable.

Below is the schematic Schematic

Below are some essential points:

  1. In the phototransistor stage, I don't understand the symbol with the Arrow on the extreme left, I thought it was a Pot set to 1K Ohm so I used a 1K resistor between the 150 Ohm resistor and +5V.

  2. My 1uF capacitor in the second stage is tantalum. My second capacitor, the 4.7uF, is electrolytic.

  3. The schematic says the pin 11 of the LM324 should be connected to -5V, since I don't know how to get -5V out of Arduino I just connected it to GND on Arduino.

  4. I did not have a IN4004 diode so I used a IN4007.

Where am I going wrong?

  • \$\begingroup\$ I see dozens of pulses. Maybe try lowering the timebase to get a better resolution. \$\endgroup\$
    – Andy aka
    Commented Dec 18, 2022 at 10:31
  • \$\begingroup\$ @Andyaka time base? Baudrate u mean? \$\endgroup\$ Commented Dec 18, 2022 at 10:32
  • 1
    \$\begingroup\$ Pot can be inadvertently set to 0 ... Diode of TCRT should not "like" this. \$\endgroup\$
    – Antonio51
    Commented Dec 18, 2022 at 10:44
  • 1
    \$\begingroup\$ That's not a "Pot set to 1K Ohm" it's a 1k pot used as a variable resistor, which you adjust to a value which makes the circuit work. Your would typically start by setting it somewhere in the middle of its range and adjusting it higher or lower as required. \$\endgroup\$
    – brhans
    Commented Dec 18, 2022 at 17:22
  • 1
    \$\begingroup\$ Please do not edit your question to invalidate previous answers. I've rolled back your question to the form that was answered. \$\endgroup\$
    – Hearth
    Commented Dec 21, 2022 at 6:34

2 Answers 2


If you need a negative voltage, you can use this (only V2- part of schematic, D2-D3-C10-C11) or use outputs of Arduino with software ...

enter image description here

  • \$\begingroup\$ I was thinking it might be easier to get -5v using an adaptor or a battery, does that make sense? \$\endgroup\$ Commented Dec 18, 2022 at 11:29
  • \$\begingroup\$ Yes, of course, you can ... for testing. Do not forget to add decoupling 100 nF for -5 V near supply pin to ground. \$\endgroup\$
    – Antonio51
    Commented Dec 21, 2022 at 4:41
  • \$\begingroup\$ Antonio51 has given the right solution, but I found to my application the use of a TC7660 IC more suitable with 10uF Capacitor (as advised on another forum). But since Antonio's answer is correct and the source for my further inquiry, that stays as the solution. \$\endgroup\$ Commented Dec 21, 2022 at 6:26

Regarding the question first part, the ideal method needs to be to check the output of each stage progressively and make alterations till that expected output is achieved. It was discovered that 1K pot was not set at 1K and needed to be altered to receive the expected output at stage 1. In this case the 1k pot needed to be turned to zero.


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