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I want to create a transimpedance amplifier with a very high gain using LM358 to...
kevinthomasajax

kevinthomasajax

@copilot I want to create a transimpedance amplifier with a very high gain using LM358 to take the output from an IR photodiode and make it readable by an ESP32
2y

copilot

Creating a transimpedance amplifier (TIA) with the LM358 op-amp to amplify the current from an IR photodiode (BPW34) and feed a readable voltage level to an ESP32 is a common approach for photo-detection projects. For a high gain, the feedback resistor value needs to be high. However, since you're aiming for "very high gain," it’s crucial to manage noise and stability. Here is how you can connect the components:
  • Transimpedance Amplifier Design:
    • Use the BPW34 as your photodiode. For an optimal response, connect it in reverse bias. This configuration improves the speed and increases the responsivity due to the wider depletion region.
    • The LM358, a dual op-amp, will be used here in a single-supply operation suitable for your ESP32's logic levels. Use only one amplifier per LM358 for this purpose.
Suggested Circuit Connections
  1. Photodiode (CELL1) to Op-Amp (U2):
    • Connect CELL1:2 (Anode) to U2:3 (+IN1).
    • Connect CELL1:1 (Cathode) to U2:2 (-IN1) and also to one end of the feedback resistance (R1).
    • You might also need to connect the anode of the photodiode to the positive supply through a high-value resistor (let's assume R2 for discussion, not included in your current project list) to ensure reverse bias and improve the response. The value of R2 could be in the range of $10 \text{k}\Omega$ to $100 \text{k}\Omega$.
    • The feedback resistor (R1) should be connected between U2:1 (OUT1) and U2:2 (-IN1). Given your high gain requirement, start with $1 \text{M}\Omega$ (R1's value might need to be adjusted based on your exact gain requirements and noise performance).
  2. Supply Voltage for LM358 (U2):
    • Connect U2:4 (V-) to U1:2 (GND).
    • Connect U2:8 (V+) to U1:1 (3V3).
  3. Output to ESP32:
    • Connect U2:1 (OUT1) to one of the ADC pins of the ESP32 for reading the voltage level. Assuming you choose pin D32 for the ADC input, connect U2:1 to U1:21 (D32).
  4. Decoupling Capacitor for Noise Reduction (optional but recommended):
    • Place a capacitor (C1) close to the LM358’s power supply pins for noise reduction. A value of $100 \text{nF}$ is typically used. So, connect C1 across U2:4 (V-) and U2:8 (V+).
  5. Output to LED (optional, for visual indication):
    • If you want a visual indication, you can use LED1 as an output indicator. This would require a current-limiting resistor (not listed in your project components). The connection would then be from U2:1 (OUT1) through a resistor to LED1:2 (A), and LED1:1 (K) to U1:2 (GND).
Please Note:
  • The actual gain of your TIA will depend on the feedback resistor (R1). You may need to adjust the value based on your sensitivity requirements and the input signal from the photodiode.
  • It's crucial to keep the layout tight, especially around the high-gain sections, to minimize noise pick-up.
  • Since a very high gain is mentioned but not quantified, I opted for a 1 MΩ feedback resistor as a starting point. Adjust based on experimental feedback and noise considerations.
Assumptions:
  • You will power the LM358 from the ESP32's 3.3V supply to keep things simple and compatible.
  • An ADC pin (D32) on the ESP32 is used for reading the amplified signal.
Feel free to adjust the values based on your testing and the specific requirements you have.
2y
5
R1
Resistance
500 Ω
CELL1
C1
Capacitance
Capacitance
U2
U3
LED1
U1

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