Serial Relay Output / Optoisolator Input

IOM #141

Peter H. Anderson
915 Holland Road, Bel Air, MD 21014,

Ordering information.


This is a fully assembled unit that is controlled by a PC COM port or similar (9600 baud, 8 data bit, no parity, no flow control).

(Mar 14, '05). Sample Liberty Basic Code for a PC (Windows). More will be added in the future.

It provides four form C relays (15A / 120 VAC, 10A / 240 VAC, 15 A / 24 VDC) with a three position screw type connector for each relay. An LED is provided for each relay such that one can visually observe the state of the relay.

Further, it provides four optoisolators, each with a two position screw type connector and LED.

The PCB is professionally fabricated.

The module includes a female DB9 connector, RS232 level shift circuitry, an on-board 5 VDC supply, a Microchip PIC processor, four relays and associated transistors and LEDs and terminal blocks, four 4N37 optoisolators and associated LEDs and terminal blocks.

Ground and Reset leads are provided on a connector. Momentarily ground to reset the processor.

A separate LED is provided which blips one time nominally every ten seconds when idle to indicate the unit is alive and blips multiple times when a command is received from the PC.

The unit is mounted on four 0.5 inch nylon standoffs.

The unit includes a coaxial power connector which will accommodate a 9 - 12VDC (2.5mmID x 5.5mmOD female center positive) wall power unit and compatible 120 VAC wall power unit.

A DB9M to DB9F through serial cable is also included.

Note that this unit is functionally the same as the IOM #142 Serial Module except that the IOM #141 does not provide a temperature measurement capability. The IOM #140 which predated the IOM #142 is no longer offered.


The intent is designing modules such as this is to involve my undergraduate students in meaningful design experiences, while at the same time providing useful low cost products for hobbyists and tinkerers.

In the spirit of this activity, I don't want people buying items that do not work for them or do not meet their expectations. Thus, this unit may be returned at any time for a full credit.

Detailed Description.

The relays are identified as 1, 2, 3 and 4. Each may be independently operated by issuing either an "N" (oN) or "F" (oFf) command. Note that a 0 operates or releases all four relays.

For example;

N1		' operate relay 1
N3		' operate relay 2
F1		' turn off relay 1
N4		' turn on relay 4
F0		' turn off all relays
N0		' turn on all relays
The processor echoes the command and provides the state of the addressed relay (or relays).

For example;

N1 1
N0 f	' note that all four relays are operated
F1 0

In addition, the state of a relay or all relays may be determined by issuing the "S" (status) command.

The processor echoes the command followed by the state or states of the addressed relay(s).
S1 0	' relay 1 is off
S4 1	' relay 1 is on
S0 e	' relays 4, 3 and 2 are on.
The state of the input optoisolators may similarly be determined using the "I" (input) command.
I1	' read input 1
I4	' read input 4
I0	' read all 4 inputs.
The processor echoes the command followed by the state of the input or inputs.
I1 0	' input 1 is at a 0
I4 1	' input 4 is at 1
I0 c	' inputs 4 and 3 are at logic one.

Ordering information.