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LamaPLC: CJMCU-8221 Analog Devices Precision instrumentation amplifier module
The CJMCU-8221 is a high-performance, gain-programmable precision instrumentation amplifier module based on the AD8221AR chip by Analog Devices. It is specifically designed to amplify small signals in noisy environments with high accuracy.
Key Technical Specifications
- Core Chip: Analog Devices AD8221.
- Programmable Gain: Set via a single external resistor from 1 to 1000.
- Supply Voltage: Supports single or dual supplies from ±2.3 V to ±18 V.
- High CMRR: Minimum Common-Mode Rejection Ratio (CMRR) of 80 dB to 90 dB (at G=1), enabling rejection of wideband interference and line harmonics.
- Low Noise: Input voltage noise of approximately 8 nV/√Hz at 1 kHz.
- Form Factor: Compact MSOP package on a breakout board for easy prototyping.
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CJMCU-8221 Pinout
| Pin # | Mnemonic | Description |
|---|---|---|
| 1 | -IN | Negative Input Terminal for the differential signal. |
| 2 | RG | Gain Setting Terminal. Connect one end of the gain resistor here. |
| 3 | RG | Gain Setting Terminal. Connect the other end of the resistor here. |
| 4 | +IN | Positive Input Terminal for the differential signal. |
| 5 | -VS | Negative Power Supply. Connect to negative rail (e.g., -5V) or Ground for a single supply. |
| 6 | REF | Reference Voltage. Sets the output “zero” level. Typically connected to Ground (GND). |
| 7 | VOUT | Output Signal. The amplified result of (+IN) - (-IN). |
| 8 | +VS | Positive Power Supply. Connect to positive rail (e.g., +5V to +18V). |
- Dual vs. Single Supply: While it can operate on a single supply (4.6V to 36V), using a dual supply (±2.3V to ±18V) is recommended to ensure the output can swing fully to zero.
- REF Pin: Do not leave this pin floating. Tie it to GND for a 0V reference or to a specific voltage if you need to level-shift the output.
- Decoupling: Always place bypass capacitors (e.g., 0.1µF) between the supply pins and ground to minimize noise.
Gain Calculation
The gain (G) of the module is determined by the external resistor (RG) connected across the RG pins. Use the following formula:
| Target Gain | Resistor (R<sub>G</sub) |
|---|---|
| 1 | Open (No resistor) |
| 10 | 5.49 kΩ |
| 100 | 499 Ω |
| 1000 | 49.4 Ω |
Many breakout boards come with a pre-soldered 499 Ω resistor, setting the default gain to approximately 100.
Arduino Code Example
void setup() { Serial.begin(9600); } void loop() { int sensorValue = analogRead(A0); // OUT Pin: Connect to an Arduino Analog Input (e.g., A0) float voltage = sensorValue * (5.0 / 1023.0); // Convert to voltage Serial.println(voltage); delay(100); }
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