View source for 7501Tx relay racks

Models 7501T8, 7501T16 and 7501T24 are solid-state relay (SSR) racks that accommodate (up to 8, 16 and 24, respectively) G4 type SSR modules. Except where specified otherwise, this document applies to all three relay rack models.

==Pinout==

{| class="wikitable" style="text-align:center;float:right;margin-left:25px"
|+ Pin function table
! colspan="6" | Relay Rack
! colspan="3" | GPIO
|-
! rowspan="2" colspan="3" | Model<br>7501Tx
! rowspan="2" | SSR<br>Socket
! rowspan="2" | Header<br>Pin
! rowspan="2" | Terminals<br>(+/-)
! colspan="2" | Model 826
! rowspan="2" | Model<br>2410
|-
! J3 !! J2
|-
| rowspan="8"  style="padding-bottom:0" | &nbsp;8&nbsp;
| rowspan="16" style="padding-bottom:30%" | 16
| rowspan="24" style="padding-bottom:30%" | 24
|  0 || 47 || 1 / 2   ||  0 || 24 || 17
|-
|  1 || 45 || 3 / 4   ||  1 || 25 || 19
|-
|  2 || 43 || 5 / 6   ||  2 || 26 || 21
|-
|  3 || 41 || 7 / 8   ||  3 || 27 || 23
|-
|  4 || 39 || 9 / 10  ||  4 || 28 || 9
|-
|  5 || 37 || 11 / 12 ||  5 || 29 || 11
|-
|  6 || 35 || 13 / 14 ||  6 || 30 || 13
|-
|  7 || 33 || 15 / 16 ||  7 || 31 || 15
|-
| rowspan="16" style="background-color:#ddd" |
|  8 || 31 || 17 / 18 ||  8 || 32 || 1
|-
|  9 || 29 || 19 / 20 ||  9 || 33 || 3
|-
| 10 || 27 || 21 / 22 || 10 || 34 || 5
|-
| 11 || 25 || 23 / 24 || 11 || 35 || 7
|-
| 12 || 23 || 25 / 26 || 12 || 36 || 41
|-
| 13 || 21 || 27 / 28 || 13 || 37 || 43
|-
| 14 || 19 || 29 / 30 || 14 || 38 || 45
|-
| 15 || 17 || 31 / 32 || 15 || 39 || 47
|-
| rowspan="8" style="background-color:#ddd" |
| 16 || 15 || 33 / 34 || 16 || 40 || 33
|-
| 17 || 13 || 35 / 36 || 17 || 41 || 35
|-
| 18 || 11 || 37 / 38 || 18 || 42 || 37
|-
| 11 ||  9 || 39 / 40 || 19 || 43 || 39
|-
| 19 ||  7 || 41 / 42 || 20 || 44 || 25
|-
| 20 ||  5 || 43 / 44 || 21 || 45 || 27
|-
| 21 ||  3 || 45 / 46 || 22 || 46 || 29
|-
| 22 ||  1 || 47 / 48 || 23 || 47 || 31
|-
|}

===Header===

The relay rack has a 50-pin header which is compatible with several Sensoray GPIO products, including models 826 and 2410.

All even-number pins are shorted together and to the GND terminal. The odd-number pins are assigned as shown in the pin function table.

Unused, odd-number pins are not connected (NC) to circuitry on the relay rack. For example, in the case of model 7501T8, odd-number pins in the range [1:31] are NC.

===Field wiring===

The relay rack includes screw terminal blocks for connecting to field wiring. Two terminals are provided for each SSR, designated "+" and "-" in the pin function table.

In the case of an AC relay, the voltage polarity across the two terminals doesn't matter. However, when using a DC relay, you must ensure that the field wiring has the correct polarity. For example, in the case of SSR2 (which uses terminals 5 and 6), the voltage at terminal 5 should never be negative with respect to terminal 6.

==Rack power==

You must supply 5 VDC operating power to the relay rack. Typically this is done by connecting an external 5 VDC power supply to the relay rack. The external power supply must share a common ground with the computer power supply.

The relay rack provides two screw terminals for this purpose, which are labeled +5V and GND. Alternatively, in some cases you may be able to obtain relay rack power directly from the GPIO board, which will allow you to omit the external power supply; refer to the sections below for details.

==Using with Sensoray 826==

The relay rack requires 5 VDC operating power, which typically is supplied by an external power supply connected to the +5V and GND terminals. Alternatively, you may modify the relay rack as follows: On the bottom of the relay rack, attach a wire (via solder) from the +5V terminal to J1 pin 49. This will use +5 V from the 826 board to power the relay rack.

Use a 50-conductor flat cable to connect the relay rack to header J2 or J3 on the 826 board. The pin function table shows the GPIO associated with each SSR. For example, if the relay rack is connected to J2 then SSR2 will be associated with GPIO26.

An output SSR is controlled by writing to the associated GPIO, whereas an input SSR is monitored by reading the GPIO. Model 826 has active-low GPIOs and the relay rack is designed for active-low signaling. Consequently, you must write '1' to turn on an output SSR and write '0' to turn it off. Similarly, when reading an input SSR, '1' indicates the relay is on and '0' indicates off.

==Using with Sensoray 2410==

The relay rack requires 5 VDC operating power, which must be supplied by an external power supply connected to the +5V and GND terminals.

Use a 50-conductor flat cable to connect the relay rack to the 50-pin header on the 2410 module. The pin function table shows the GPIO associated with each SSR. For example, SSR2 is associated with GPIO21.

An output SSR is controlled by writing to the associated GPIO, whereas an input SSR is monitored by reading the GPIO. Model 2410 has active-low GPIOs and the relay rack is designed for active-low signaling. Consequently, you must write '1' to turn on an output SSR and write '0' to turn it off. Similarly, when reading an input SSR, '1' indicates the relay is on and '0' indicates off.