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Functional overview
The tracker continuously balances the light on two LDRs. When the illumination is unbalanced, the differential voltage is amplified by the TDA2822, which applies a polarity across the motor that turns the panel until the LDR voltages equalise (error ≈ 0), whereupon the motor stops.
Complete block diagram
Sunlight
│
┌───────────▼───────────┐
│ LDR SENSOR ARRAY │ (LDR-EAST, LDR-WEST)
└─────────┬─────────────┘
│ V_E, V_W
┌────────────▼─────────────┐
│ VOLTAGE-DIVIDER STAGE │ (10 k–100 k fixed / trim resistors)
└────────────┬─────────────┘
│ Differential voltage (ΔV = V_E − V_W)
┌────────────▼─────────────┐
│ DEAD-BAND / FILTER │ (R-C, trimmer pot or Op-amp window)
└────────────┬─────────────┘
│ Vin1 Vin2
┌────────────▼─────────────┐
│ TDA2822 (BTL) │
│ Dual power amplifier │
│ acts as bidirectional │
│ motor driver │
└────────────┬─────────────┘
│ OUT1 OUT2
┌────────────▼─────────────┐
│ DC GEARED MOTOR │ (5-9 V, ≤0.8 A stall)
└────────────┬─────────────┘
│ Torque
┌────────────▼─────────────┐
│ PANEL MOUNT & GEARING │ (single-axis pivot)
└────────────┬─────────────┘
│ Mechanical feedback
─────────────┴─────────────────────────────────────────────
┌─────────────────────────────────────────────────────────┐
│ POWER MANAGEMENT │
│ PV module → blocking diode → battery → 5–9 V LDO/DC-DC │
│ Decoupling (100 nF || 10 µF) at IC, fuse, reverse prot.│
└─────────────────────────────────────────────────────────┘Theoretical foundations
• LDR resistance follows approximately \(R_L = k\,E^{-\gamma}\) (E = illuminance).
• Voltage divider outputs: \(VE = V{CC} \frac{R{FE}}{R{FE}+R{LDR,E}}\). The motor sees \(V{M} = V{OUT1} - V{OUT2} ≈ A\,(V_E - V_W)\).
• In BTL, the TDA2822 can deliver \(VM ≈ 2(V{CC} - V_{sat})\), doubling available motor voltage compared with single-ended drive.
Practical applications
• Educational demonstrators, garden lights, small 1–10 W PV panels.
• Not recommended for large (>30 W) panels because the TDA2822 is limited to ≈1 A peak and ≈15 V max.
Motor drive with TDA2822
• Bridge-tied load connection: motor between OUT1 and OUT2, inputs fed by V_E and V_W.
• Add 1 Ω–2.2 Ω current-sense resistor in series if current limiting is required.
• Free-wheel diodes are unnecessary because the H-bridge outputs already provide a conduction path, but a RC snubber (0.1 µF-100 Ω) across the motor suppresses EMI.
Dead-band / hysteresis
• To avoid hunting, introduce ±50 mV window using a trimmer between the two sensor nodes or add an LM358 window comparator whose outputs drive the TDA2822 inputs.
Component example table
| Block | Typical parts | Remarks |
|---|---|---|
| LDR array | GL5528 LDR ×2 | 10–50 kΩ @ 10 lx |
| Dividers | 10 kΩ fixed + 10 kΩ pot | adjust symmetry |
| Dead-band | 10 k pot + 100 nF | sets threshold |
| Driver | TDA2822D or TDA2822M | DIP-8/SO-8, heat-sink tab ground |
| Motor | 6 V 60 rpm gear motor | stall ≤0.8 A |
| Supply | 6 V-9 V, 1.5 A | from battery / buck |
Mechanical
• Counter-balance panel to reduce motor torque.
• Use worm gear to provide self-locking (prevents back-drive at night).
Electrical
• Keep sensor and power grounds common; star-wire supply to minimise crosstalk.
• Add 0.47 µF bootstrap capacitor between pins 1-3 of TDA2822 as per datasheet for BTL stability.
Calibration & test
• Cover one LDR → verify correct motor direction; swap inputs if reversed.
• Measure motor current with ammeter; ensure < 1 A.
• Thermal-run test at midday; IC case should stay < 70 °C.
A TDA2822-based solar tracker is feasible for small, low-power panels: LDR voltage dividers create an error signal, the TDA2822—wired in BTL—amplifies this differential and drives a modest DC gear motor until alignment is restored. While inexpensive and simple, its current and voltage limits confine it to demonstrators; modern trackers usually adopt microcontrollers and stronger H-bridges for higher reliability and efficiency.