PCB

[LigasN]

All parts, documentation, and stuff about the PCB project.

[LigasN]

Light connector:
Degson - DG308-2.54-02P

[LigasN]

The voltage regulator for Raspberry supply needs to have parameters:

output current - 1.34 it is better for Raspberry to have 2,5A (producer said that)
input voltage - 3.7V * 4 batteries in series = 14.8V
output voltage - 5V or a little more like 5.2V

[LigasN]

[LigasN]

Resign from internally configured LM1085, because there is possible to set up 5.2V for Raspberry board supply and have light power control.

[LigasN]

This can be better: https://botland.com.pl/przelaczniki-dzwigienkowe/8392-przelacznik-dzwigniowy-on-off-kn3c-101-250v-6a-5904422311674.html

Then with connector: https://botland.com.pl/zlacza-ark/2554-zlacze-ark-raster-35mm-2-pin-5szt-5904422353346.html

[LigasN]

Bipolar transistor to turn on/off 12V supply for lights:
CDIL Semiconductors BCW66G NPN 0,8A, 45V, 330mW
https://static1.squarespace.com/static/5416a926e4b09de8832655bc/t/5d42ad2b5cccc300011e8b63/1564650797776/BCW66F_G.PDF

[LigasN]

https://www.electricalelibrary.com/en/2018/07/02/how-to-polarize-the-bjt-transistor-part-1/

Ib = Ic(sat) / hfe
Rb = (Uin-Vbe)/Ib

Ic(sat) = 10mA, hfe = 110
Ib = 91uA -> Rb = (3.3 - 0.7) / 91u = 28571 Ohm

Ic(sat) = 30mA, hfe = 120
Ib = 250uA -> Rb = 2.6 / 250u = 10400

[LigasN]

Capacitors:

• tantalum: https://www.piekarz.pl/30602-kondensator-avx-10uf-16v/

[LigasN]

Soo, the next battery:
https://botland.com.pl/akumulatory-li-ion/9066-ogniwo-18650-xtar-2200mah-6952918341307.html
basket: https://botland.com.pl/koszyki-na-baterie/5240-koszyk-na-2-akumulatory-typu-18650-polaczenie-szeregowe-5904422374341.html

[LigasN]

better charger: https://botland.com.pl/ladowarki-do-akumulatorow-i-akumulatorkow/8543-ladowarka-akumulatorow-xtar-mc2-18650-6952918320197.html

[LigasN]

connector https://botland.com.pl/zlacza-ark/2554-zlacze-ark-raster-35mm-2-pin-5szt-5904422353346.html

[LigasN]

Voltage stabilizer adjustable 3A: https://www.ti.com/lit/ds/symlink/lm1085.pdf?ts=1652640073874&ref_url=https%253A%252F%252Fwww.ti.com%252Fstore%252Fti%252Fen%252Fp%252Fproduct%252F%253Fp%253DLM1085IT-ADJ%252FNOPB%2526keyMatch%253DLM1085IT-ADJ

[LigasN]

Vout = 1.25V(1+(R2/R1))
Vout is adjustable by R2 so:

• Vout min = 1.25V
• Vout max > 4 * 3.7V
• R2 > 1.2 kOhm

[LigasN]

For raspberry 5.1V will be done by:
Vout = 1.25(1 + (R2/R1)), R2 = 330 + 39, R1 = 120
Vout = 5.09V

[LigasN]

potentiometer: https://www.piekarz.pl/05977-potencjometr-rm065-rm-p2-5x5-202/

[LigasN]

The potentiometer is needed to make it possible to investigate light problems with weaker light sources as it is the prototype of the stand.

[LigasN]

Shop list:

• 2 x LM1085IT-ADJ
• Potentiometer 2KOhm
• 4 x Tantalum capacitor 10uF
• 1 x Resistor 330Ohm
• 3 x Resistor 120Ohm
• Raspberry long connector(both side)
• 8 x Resistor 100Ohm
• 8 x NPN Transistor
• 2 x Lights connector
• 3 x ARK connector
• DC Connector
• 2 x Battery socket
• 4 x Battery
• Switch

[LigasN]

[LigasN]

1. It works with a 47k resistor between input and output light source cables. It works because of the current divider rule (The first Kirchhoff rule).

[LigasN]

2. The second problem was caused by two things. First, was ammeter connected right before raspberry (no idea why it is wrong but it causes rebooting). The second was too much difference between input and output voltage. I am measuring current now by connecting the ammeter after batteries. The second problem can be fixed by connecting the step-down voltage regulator for raspberry to two accumulators connected in series only. The second pair will be used only for light sources.

[LigasN]

The step-down voltage regulator is heating anyway so there should be a radiator or sth attached to it.

[LigasN]

One more thing is to connect the pin via a resistor to the ground, to ensure pin states.

[LigasN]

1. Problem occurs to be not true. After replacing the transistor it works well.

[LigasN]

[LigasN]

To-do list before printing PCB:

• Calculate and check the pull-down resistor value
• Add pull-down resistor to schematic
• Change the Raspberry voltage regulator and buy
• Test new DC/DC converter for Raspberry
• Update schematic for the Raspberry supply
• Update board project

[LigasN]

Raspberry supply voltage regulator: https://www.tme.eu/Document/949639eab2f7194baeac95dcad7e2dd3/AP1507x-DTE.pdf

[LigasN]

Raspberry supply voltage regulator in the shop: https://www.tme.eu/pl/details/ap1507-d5-13/regulatory-napiecia-uklady-dc-dc/diodes-incorporated/

[LigasN]

Diode:
https://www.mouser.pl/datasheet/2/427/ssb43l-1767997.pdf
https://www.tme.eu/pl/en/details/ssb44-e3_52t/smd-schottky-diodes/vishay/

| Load current | 4A |  
| Max. forward voltage | 0.49V |  
| Case | DO214AA |  
| Kind of package | reel,  tape |  
| Max. forward impulse current | 100A |

[LigasN]

Calculations based on:
https://passive-components.eu/how-to-choose-the-right-inductor-for-dc-dc-buck-applications/?fbclid=IwAR3pjfMoje9W4Bx9vYtv5tKTdSNtyyKmopRzp0mcMnkpt9_t6x7gcEN-igE

https://www.analog.com/media/en/technical-documentation/data-sheets/ADP2302_2303.pdf?fbclid=IwAR0of-30OkK2Es2K5xtyRGCRMzyIjKZQX6vp88xYeUHGSZ0HtwGLhMZivGw

[LigasN]

Inductor:
https://www.tme.eu/Document/0a0a45af3542fdef69db0e033325315b/HPI1040.pdf
https://www.tme.eu/pl/en/details/hpi1040-220/smd-power-inductors/ferrocore/

[LigasN]

On input 2x 100n and 2x 4,7u all in parallel, on output 2x 22u in parallel as well.

• 2x 100nF
• 2x 4,7uF
• 2x 22u

[LigasN]

The new power supply for Raspberry works fine. There is no heat problem. Below is an image of raspberry with the camera and LED turned on.

[LigasN]

For good output value 5.1 < Vout < 5.2, R1 was 7,27kOhm and R2 = 2,39kOhm

[LigasN]

Pull-down resistor calculations

[LigasN]

Some stuff measured on the prototype board:

• Ic - 67mA
• The transistor needs at least Ib > Ic / Hfe(~200) = 335uA. Value is confirmed via simulation in the LTSpice project and on the PCB board.
• Vbe = a little bit more than 0.7, like 0.76V

[LigasN]

Calculations with electricalelibrary:
Ic(max) = (Vcc - Vce(sat))/Rc => Ic(max) = (12V - 0.3V) / 150Ohm = 11.7V / 150Ohm = 78mA (measured before min. 60mA - max. 67mA)

Ib min = Ic(sat) / hfe => Ib = 100mA (> 67mA to ensure correct work and its datasheet example value) / 200 (it was measured on PCB, should be around the correct value) = 500uA

Rb max = (Vin - Vbe) / Ib = (3.3V - 0.7V) / 0.5mA = 5200 Ohm, so I tested 4.3kOhm and I got 565uA.

[LigasN]

For the pulldown resistor, I've checked that 10KOhm works just fine. From a couple of Internet sources, I have got to know that for raspberry powered by a battery it is even better to put a higher value resistor. So I decided to use 22kOhm. It makes 3.3V / 22kOhm = 15uA.

[LigasN]

Schematic

Board