Embedded PIC Module

By: Pmb  06-Dec-2011


The SIM_1A is available as a general purpose embedded PIC project board. With a bit of programming it can be a very powerful little controller of only 64mm x 39mm x 22mm.

It includes a surface mount PIC16F876A with a 20MHz crystal as standard. Most of the I/O connections are via a 40-pin box header which accepts an IDC plug and ribbon cable. We can also supply it with a dual-row right-angle or straight header pin strip for circuit board mounting. The serial port, power and a few I/O connect via miniature screw terminals.

The SIM_1A was designed recently to be a networked I/O moduleas part of our PMBACS control system. Multiple SIM_1A modules can connect via a single CAT-5 or security cable to a master controller. The SIM_1A provides local I/O connections, some preprocessing and then transfers data to the master. The screw terminal connections are for connecting field wiring that can be run some distance from the SIM_1A without additional protection. The 40-way header is intended for local I/O that does not run far from the board; typically switches, LEDs, light sensor, temperature sensor etc.

If you want to interconnect SIM_1A boards We can provide a starting point for networking and a simple protocol and the rest is up to you. We're not currently providing full network support software but may do so at a later date. We are currently developing an upgrade to our existing simple network.

The SIM_1A can be powered from 12V DC supplied via the screw terminals. This configuration allows a number of SIM_1A boards to be connected together on a single cable forming a simple network. The boards are powered and communicate over the one cable. The maximum length possible depends on the type of cable and the loading at each board.


  • double sided, plated through circuit board

  • mostly surface mount componentry
  • on-board smd PIC16F876A microcontroller running at 20MHz
  • 5-way pin header for ICSP programming
  • on-board green status LED
  • small size, 64mm x 39mm x 22mm
  • operates from 9V to 15V DC
  • typically draws 10mA (more depending on I/O connections)
  • 40-PIN IDC local I/O connection
  • 10-way miniature screw terminals for field wiring
  • analog inputs, digital I/O and two high current outputs
  • resistor and resistor/capacitor protectionon local I/O
  • resistor/capacitor/zener protection on field I/O


The on-board I/O includes:

  • one serial communications port (connected to the 16F876 uart)

  • two high current mosfet outputs switching to 0V
  • four digital low level I/O via the 40-way header
  • two digital low level I/O via the screw terminals
  • four analog inputs or digital I/O via the 40-way header
  • one analog input or digital I/O via the screw terminals
  • eight low level digital outputs via the 40-way header
  • five lines providing I/O expansion via the 40-way header (serial expansion)

The eight low level digital outputs are provided by an on-board 74HC595 serial to parallel latch. These can be used to directly drive LEDs. A simple software routine is required to update the outputs.

The same CPU lines that drive the on-board 74HC595 are available via the 40-way header. This allows the number of outputs to be increased off-board by adding additional 74HC595 chips. Additional inputs can be added using a similar parallel to serial interface chip.

The high current outputs can handle an amp or so each. The power supply and connections must be rated to handle the current. The outputs are mosfet switched to 0V (ground). These outputs can be used to switch loads up to an amp or so at 12V. They are suitable for controlling door locks, lamps and alarm sirens.

By "low-level" we mean 0 to 5V logic level signals. All I/O lines within the 40-way header include on-board series resistance to provide some protection of the on-board circuitry. This also allows the outputs to directly drive LEDs without an external resistance.

The 16F876A serial port is available at the screw terminals. These lines are protected on-board by an R-CZ-R arrangement and can be run some distance without additional protection. The serial RX and TX lines are at 0 to 5V levels. For connection to a PC serial port a level converter such as a ST232 or MAX232 will be required.

A 5-pin single row header allows simple In-Circuit-Serial-Programming. A 5-pin Molex single row 2.54mm pitch plug is required to connect for programming. The header provides connection to ground, +5V, data, mclr, and clock (- + D M C) in that order. Power should be applied to the board for programming. It's unlikely the ICSP programmer will be able to power the board during programming.


The I/O have been labeled A, B, C, D and Z:

  • A1 to A4 are local analog capable inputs or could be used as digital I/O lines (100R, 0.1uF and 1K).

  • B1 to B4 are local digital I/O lines (100R, 10pF, 1K).
  • C1 to C8 are local digital output lines. (470R series resistor only).
  • C9 and C10 are the high current outputs, rated 1A 24V DC.
  • D1 is a field wiring digital input with an internal 1K pull-up to +5V.
  • Z1 is a field wiring digital input (zone input).
  • Z2 is a field wiring analog input (zone input).

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