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µS-RL4 Relay Board User Manual


The µS-RL4 is designed to allow easy connection of four SPNO (Single Pole Normally Open) relays to a µStack system. Each relay is controlled by one of the µStack I/O lines configurable by jumper. It is therefore possible to use up to four relay boards on a µStack system. Note that when using an RL4 board the µStack should ideally be powered from a 12V D.C. source.

Status LEDs

Each relay on the RL4 has an associated status LED which is ON when the relay is energized.

µS-RL4 Configuration

The µS-RL4 configuration is by jumper selection. A jumper link between J3 and J4 selects the µStack I/O line which control each relay. Note that it is important not to attempt to control a single relay with more than one I/O line, therefore great care should be taken to ensure that a single relay is not selected twice.

Use of the µS-RL4 with Mains Voltages

While both the relay and connectors used on the µS-RL4 are mains rated, safe connection to hazardous voltages is highly installation specific. You should not connect the µS-RL4 to voltages greater than 40V A.C. unless you are qualified to do so and have ensured that all relevant safety standards are met.


µS-RL4 Configuration Jumpers

P15/RL4  (Link to control RL4 with P15)
P14/RL3  (Link to control RL3 with P14)
P13/RL2  (Link to control RL2 with P13)
P12/RL1  (Link to control RL1 with P12)
P11/RL4  (Link to control RL4 with P11)
P10/RL3  (Link to control RL3 with P10)
P9/RL2  (Link to control RL2 with P9)
P8/RL1  (Link to control RL1 with P8)
P7/RL4  (Link to control RL4 with P7)
P6/RL3  (Link to control RL3 with P6)
P5/RL2  (Link to control RL2 with P5)
P4/RL1  (Link to control RL1 with P4)
P3/RL4  (Link to control RL4 with P3)
P2/RL3  (Link to control RL3 with P2)
P1/RL2  (Link to control RL2 with P1)
P0/RL1  (Link to control RL1 with P0)


Technical Specification


: 4 SPNO relay

Output Rating

: 5A @ 250V A.C., 30V D.C.


: 0-5V 2.5mA per channel

Power In

: 10V-14V DC. 160 mA nom.




µS-RL4/µFlash 876 test program

// Sequentially energizes each of the relays for 1 sec.
// Assumes uS-RL4 configured for relay control using P12-P15      
// Compile with CCS PICC (PCM/PCW)
#include <uF876.h>
void main(void)
    while(true)                   // Repeat forever
        output_low(P12);          // Relay 1 OFF
        output_high(P15);         // Relay 4 ON
        delay_ms(1000);           // Wait 1 Second
        output_low(P15);          // Relay 4 OFF
        output_high(P14);         // Relay 3 ON
        delay_ms(1000);           // Wait 1 Second
        output_low(P14);          // Relay 3 OFF
        output_high(P13);         // Relay 2 ON
        delay_ms(1000);           // Wait one Second
        output_low(P13);          // Relay 2 OFF
        output_high(P12);         // Relay 1 ON
        delay_ms(1000);           // Wait 1 Second



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