Multi Sensor PLC


The ATmega328 PLC is a credit card controller packed with many useful functions. It is light weight, consumes low power, has a DIN rail case, build in display, backup power and is scalable. With this PLC you can build and control anything you like. Compared with other PLC’s there is no need for special power supplies, or other interface modules. Practically any sensor from any manufacturer can be connected. On top of all this it is cheap compared with others PLC’s in the market.

The PC has various interfaces which are configurable depending on the use of sensors and applications

  • 4x digital IO/PWM protected .
  • 4x 10Bit Analog in protected
  • 1x Digital Power output 1Amp/li>
  • 2x DAC 12bit 0..10V 1.0 Amp powerout.
  • 1x SPI 1Mhz.
  • 1x I2C 400Khz.
  • 1x relay 120Vac 10Amp.
  • 1x SSR relay with zero detection 120Vac 10Amp.
  • 1x RS485 interface local network

  • 1x 12Vdc male Power Jack
  • 1x WIFI internet NTP/MQTT/Email/HTTP
  • 1x LCD display 4×20
  • 1x RTC 2 PPM acurate
  • 1x 256KB non volatile memory
  • 2x push buttons
  • 1x Mini USB connector
  • 1x IO matrix min header

Combined with the DIN rail based Central panel solution this PLC can give very compact control over your processes.
The picture below shows the PLC as monitor and measuring device of the electricity grid. This application can activate generators and backups at times when the CFE has blackouts. ( Grid values are zero because the photo is for demonstration purpose).

The ATmega328 PLC

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The inside

The PCB is a high quality double layer made of glass fibre, 1.5mm thick, routing is done with 10mil traces. The PCB measures 100×68 mm has 85 components, the enclosure measures roughly 107x88x60 mm.

Below an image of the PCB layout and the various functions and interfaces.


The ATmega328 PLC

The idea behind it

This PLC was developed for different reasons. One reason was to generate a flexible control platform with a display integrated to control any process you like. A second reason was to offer a complete integrated PLC solution to any one like students professionals and engineers. With this PLC you can focus on your job instead of being busy how to assemble and install a PLC controller.

The basic idea regarding the specifications for the PLC was:

  • It had to be small in size with a low power consumption
  • Should run from solar panel and or standard Lithium or lead acid batteries.
  • It should have build in AC power drivers.
  • Had to be expandable or scalable.
  • Standardized Interfaces and there for sensor manufacturer independent.
  • Equipped with a large display
  • Memory to store statistic measurements.


This controller platform has a number of applications. Some are available  and some are in a concept phase of development. Holamex works on the following applications.

  • Photo voltaic energy monitor
  • Smart solar collector differential thermostat
  • Battery heath monitor and charger.
  • Swimming pool controller with automated pool and garden light timer
  • Load control for factories with high energy demand.
  • Light lux meter.
  • Flow meter
  • High way traffic density counter.
  • Smart Solar light post monitor and battery maintenance.
  • CFE grid monitor with backup switch functionality.
  • Air pollution monitor.


The following functions are implemented

  • Central controller, ATmega328
  • RTC, Real Time Clock with high accuracy, DS3231,
  • Non volatile RAM, AT24C256, 64KB
  • RS485 half duplex bus, MAX485
  • ADC external reference, multi turn pot meter
  • Temperature sensors, DS3231, ATmega328
  • Push buttons.
  • LCD Display 4×20.
  • External Terminal port / PC interface

Ports on the module

The ports on the PLC allows connecting external sensors or measurement modules. Some of the ports provide beside the GPIO signals also the necessary power to feed the external modules or sensors.  The ports are implemented with 3.81 mm pitch screw terminals. The following ports are available:

General IO ports 2 GND, 5/12V, 2 IO’s
Analog out port 1 GND, 5/12V, 2 12bit Analog out
Relay port 1 NC or NO contact 8A,  250VAC
DC out  port 1 12VDC, 1ADC
120V power port 1 Phase cutting 120VAC, 4A
ICSP port 1 In Circuit Serial programming ICSP

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