Solar tracker PCB

This project contains solar tracker PCB I made for my dad's project.

3D Model, Front View:

3D Model, Bottom View:

Schematic:

I used KiCAD 4.0.7 for this PCB, but it should open fine in different versions, as I keep -cache.lib file in this repo.

Original schematic can be found in doc/scheme.jpg. Things that I changed:

properly terminated unused OPAMP parts
added limit switches connection

Schematic explanation

LDR1 and LDR2 photo-resistors yield signal which is used to determine in which direction PV unit (solar panel) should be rotated, i.e. in which direction we have more light radiation.

Signal from photo-resistors is being compared further by comparators built on U1A and U1B OPAMPs. Reference voltage level is generated by dividers built on R1, R2 resistors and RV1, RV2 trim-pots.

RV1 trim-pot is used to adjust this reference voltage point, so that motor stands still when both photo-resistors are receiving the same light level. RV2 is used to setup hysteresis level, so that motor is not moving when the light difference on photo-resistors is small.

H-bridge formed by Q1-Q4 transistors is powering the motor, according to control signals from comparators. Transistors are working in switch mode, as comparators yield only 0 or VCC:

V_out = 0,   if V+ < V-
V_out = Vcc, if V+ > V-

D1-D4 are just flyback diodes, providing the path for back EMF discharge from motor's coil, preventing other elements from it (transistors can be burnt, or limit switches can be carbonized due to arcing).

C1 provides some of the energy required by the motor during the initial spike of each turn-on.

R3 and R4 are used to properly terminate unused OPAMPs (U1C, U1D).

J5 and J6 terminal blocks (along with D5, D6 diodes) are used for connecting the limit switches.

Power consideration

Power voltage: 9V must be used. It's because the motor will receive only Vcc - 2.6 Volts, due to voltage drop across transistors and also on OPAMP, as it's not Rail-to-Rail one. MG995 requires the voltage to be 4.8V ... 7.2V, so the voltage drop must be accounted for.

Power current: 2A or more. Because MG995 can consume up to 1.5A on start ("stall current").

In case when 12V battery is used (it's common in solar panels appliance), I suggest one to use external 12V-to-9V buck converter (2A rated, or more). It's efficient (95%), small enough, and usually costs only $2-$3. No need to over-complicate tracker schematic by adding voltage regulator scheme to it.

Limit switches

doc/limit-switch/ directory contains two possible schemes to implement limit switches in H-bridge, with pros/cons overview. I personally like the second scheme the best, so I implemented it in this project.

EMI note

Notice that switching of DC motor's brushes leads to EMI, which may affect your external circuits (especially digital ones, like MCUs). In that case you should install EMI suppressor on your motor leads.

Prepared files

out/ directory contains ready to use files for manufacturing the PCB.

Toner Transfer Method

See out/toner-transfer-method/ for ready to use files.

Notes:

Remove the copper pour from both sides of PCB
Notice the Vias and front layer tracks. You need to solder jumper wires instead of them, in case if you are using single sided copper clad board.

Manufacturing at plant

You can order the PCB to be manufactured on plant, e.g. at Seeed Studio (Fusion PCB) or JLCPCB. Gerber files and drill file are prepared at out/gerber/.

References

Authors

Sam Protsenko

License

This project is licensed under the GPLv3.

joe-skb7/solar-tracker-pcb