MICRO CONTROLLER CIRCUIT DESIGN AND PCB DEVELOPMENT

I'm looking for an experienced circuit designer to assist in the development of a functional PCB following correct procedures and best practices.
I will require advice from you as I will only be supplying limited details.
You will need to access if any ancillary components are required, such as pull ups/downs, decoupling etc.
The PCB front print is to be kept as small as reasonably possible.
- Brief This PCB will be used in 2 modes, Master and Slave.
Master The master will be powered via a 12v regulated DC power supply.
It will also connect an external 12v device (NAYAX) and a 5v (LCD) on I2C.
Slave The slave will be powered via a 16.
v Li-Ion battery, there will be no external 12v device connected and no LCD display.
We require this mode to have a VERY low quiescent current, so this should be your primary focus in this design.
The input voltage range will be between 11.
v and 16.
v.
The DC to DC circuit must provide a stable 5v and 12v line.
However the 12v will be unused on the slave so if it helps with the quiescent current, there could be a jumper to disable the 12v ? - Main Components ATMEGA 328P NRF24L Channel Analog Multiplexer (possibly CD74HC bit SIPO register (possibly SN74HC way DIP/DIL switch screw terminal blocks.
1x2 way, 2 x 8 way - Connections +NRF24L01 (5v) Maybe the best option to purchase these devices as pre built boards (see attachment) and have them connect on to the PCB via a 2x4, 8 way header plug.
+CD74HCv) All inputs are PULLED LOW C0 - C7 = External inputs (8 way screw terminal block, see attachment) C8 - C16 = DIP/DIL inputs +SN74HCv) Q0 - Q7 = External outputs (8 way screw terminal block, see attachment) These outputs are driving LED, so could resistors placed on all outputs, or a resistor network.
+8 way DIP/DIL switches Held low, ACTIVE HIGH +MCU (5v) The ATMEGA328, needs to be removeable, so possibly the SPDIP package in a push fit connector.
0 - RX (2 way pin header) 1 - TX (2 way pin header) 2 - NRF24L01 IRQ * 3 - NAYAX IRQ ** 4 - CD74HC S0 5 - CD74HC S1 6 - CD74HC S2 7 - CD74HC S3 8 - CD74HC EN 9 - NRF24L01 CE * 10 - NRF24L01 CSN * 11 - NRF24L01 MOSI * 12 - NRF24L01 MISO * 13 - NRF24L01 SCK * 14 - SN74HC595 LATCH (Pull up 5v) 15 - SN74HC595 CLOCK 16 - SN74HC595 DATA 17 - NAYAX EN ** (Pull down GND) 18 - LCD SDA *** 19 - LCD SCL *** 20 - Voltage divider to read input (battery) voltage 21 - CD74HC SIG * 2x4 8 way female header, to correctly match NRF24L01 pinout (attached) ** Some 4 way connector, requires 12v and GND (possibly male pin header) *** Some 4 way connector, required 5v and GND (possibly male pin header) - Power 2 way screw terminal block (see attachment).
Powered from an external Li-Ion battery with a voltage up to 16.
volts.
So there will need to be some circuit to step this down to 5 volts AND 12 volts.
NOTE the quiescent current of the DC to DC circuit must be as low as possible.
The input should be protected from reverse polarity.
-Voltage Divider We need to monitor battery voltage and since the ATMEGA can only cope with 5v you will need to have a voltage divider circuit.
See attached document from ChatGPT on this.
Layout PCB Eletrônica Engenharia Elétrica Microcontrolador Design de Circuito ID do Projeto.
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