Connecting GPIO Devices to Impinj R700 RAIN RFID Readers 

 

This article covers connecting devices to the General Purpose Input/Output (or GPIO) port on the Impinj  R700 RAIN RFID reader. 
 
The Impinj R700 reader includes a multipurpose I/O port that provides two general purpose inputs, three opto-isolated outputs and a +5V supply. Access to these features is offered through a 9-pin connector mounts on the backside of the reader. In order to use this 9-pin connector, you will need a GPIO terminal block. The GPIO connector is a Phoenix Contact MC 1,5/ 9-G-3,81 modular connector, which also goes by the part number 1803345. Use this part name/number when looking for a compatible terminal block. 

Impinj R700 GPIO Information and Specifications

In order to protect the reader’s CPU, both the input and output signals are optically isolated from direct connection to the CPU. The following chart shows the electric specifications of the Impinj R700 reader's GPIO: 

Inputs 

Logic 0 (LOW)        0.0-0.8 Volts 

Logic 1 (HIGH)       3.0-30.0 Volts 

Outputs

Current                 

  • Up to 1.5A, source or sink 

Supply Voltage     

  • 5 to 30 Volts (Reference to  V MINUS)
  • Voltages > 5 Volts require an external power source connected to V PLUS and V MINUS 

Logic 0 (LOW)      

  • 0 to 0.5 Volts (Reference to V MINUS) 

Logic 1 (HIGH)     

  • VPLUS - .5 Volts 

 

For the GPIO outputs to function, a power supply must be connected between V+ and V-. This power supply could be the reader's 5V supply line and Reader GND, or an external power supply that is greater than 5V. The maximum voltage, as shown in the table above, is 30V. When the user configures a selected GPIO output via LLRP to output logic 0, an isolated FET switch within the reader effectively shorts that output to V- with a current sink capability of up to 1500 mA. 
 
When the user configures a selected GPIO output to logic 1, the selected output is pulled to V+ through a 10K resistor. If GPIO isolation is not required, the reader provides a 5V supply and a ground pin on the connector that can be connected to V+ and V-. 
 
Please note that attaching a light stack or other output device that requires the reader output to sink more than 1500mA will result in unrecoverable damage to the reader and is not covered by warranty, as it's outside the specified operating parameters. 

 
The pin orientation is shown in the image below, where PIN 1 is the left-most pin: 

mceclip0.png


Example - Testing Basic Functionality with
Impinj ItemTest Software 

One easy way to test out the GPIO functionality of the Impinj R700 is by connecting one of the reader's GPOs to a GPI. This way, you can configure the reader to start and stop the inventory based on a GPI trigger, and manually trigger the GPO through Impinj ItemTest software. 
 
To wire this, you can connect the following: 
 
Reader's 5V Supply (PIN1) to VPLUS (PIN9) 
Reader's GND (PIN2) to VMINUS (PIN8) 
Readers GPI1 (PIN3) to GPO1 (PIN5). 
 
This works, as when using the reader's 5V Supply, the GPO's Logic 1 will be 4.5V (VPLUS minus .5V), which will trigger the GPI1 to HIGH (GPI Logic shows anything greater than 3.0 V is registered as Logic 1 (HIGH)). 
 
In Impinj ItemTest software, you will want to configure the GPI Configuration for Port 1 to Start when the level is HIGH, and to STOP when the level is LOW, as shown in below screenshot: 
 
1.png

After saving these settings, we can use the Impinj ItemTest software’s Diagnostics tab to turn GPO1 to HIGH, which will start the reader inventory: 

2.png

You can confirm the inventory has started by checking the antenna LED's on the reader, and ensuring they are turning on, as well as the inventory LED on the front of the reader. 

Example - Connecting a 24V Stack Light with External Supply 

A common example is using the Impinj R700 to control a stack light. Often times, these stack lights require a 24V input, meaning an external power supply is needed as the reader is only able to provide 5V maximum. 
 
The diagram below shows an example of wiring a stack light with an external power supply: 
 
3.png

An example showing the physical wiring and implementation is shown below: 

 4.png5.png

The wiring is as follows: 
 
Green: GPO connected to light stack's green LED. 
Orange: GPO connected to light stack's orange LED 
Red: GPO connected to light stack's red LED 
Yellow: Ground cable coming from the light stack 
Black cable: External power supply, ground connection 
White: External Power supply, positive connection 

 

In this example, I am using a 24 V external power supply with a barrel adapter to separate the positive and negative terminals. 

I am controlling the Impinj R700 GPOs and setting them all to HIGH through Impinj ItemTest software, as shown here: 
 
6.png

 

Example - Connecting an IR Sensor with External Supply 

Another common use case is connecting an input switch to the reader's GPI. In this example case, we will connect a Photoelectric Sensor (any sensor that uses more than 5V should work fine).
 

The sensor we are using is shown below: 

7.png
 
The wires from the sensor are described below: 
 
Pink Wire - Control wire over Dark Mode or Light Mode 
Brown Wire - Sensor's V+ 
Black Wire- IN1 
Blue Wire- Sensor's V- 

There are two modes that the light sensor can work in, Dark-On and Light-On mode. In Dark-On mode, when the sensor sees light, it will go to high and vice-versa for Light-On mode. In my testing case, I used the Light-On mode. I have included circuit wiring diagrams below: 

8.png

82.png

 

Since we are using an NPN based sensor model, as shown in the datasheet, we will need to make sure there is a load resistor in place between the IN and VCC port, as to limit the current. This protection implementation is shown in the figure below: 
 
9.png

 
For wiring this input sensor to the Impinj R700, I used the following wiring: 

PIN3 (USERIN_0) - Connected to black wire from input sensor 
PIN8 (VMINUS) - Connected to external supply's V- and the sensor's V- 
PIN9 (VPLUS) - Connected to external supply's V+ and the sensor's V+ 
 
101.png


For this specific sensor, we also needed to connect a current limiting resistor between the USERIN_0 and the V-. 
 
To test this scenario using Impinj ItemTest software, I configured the reader's GPI to trigger when the device goes HIGH, and to stop when going LOW: 
 
11.png

 

Example - Connecting Sensor using Reader's 5V Supply 

Some input sensors will require only 5V or less to operate, so that you can use the reader's 5V supply to power. For this use case, you can use the following configuration: 
 
12.png 

The reader's 5V (PIN1) will be connected to both VPLUS (PIN9) and the User Input(s) (PIN3/4). The reader's ground connection (PIN2) will be connected to VMINUS (PIN8). 

You can test this functionality as mentioned in the section above, by using ItemTest and configuring the GPI triggers appropriately: 

13.png
 
Please note, that if using multiple GPI's, the ROSpec will only be able to assign to a single GPI. Additional GPI logic will need to be added programmatically to your code, though it is still useful to use Impinj ItemTest software to ensure both GPI connections are working properly. We provide an example showing how to use event handlers to process GPI events in the Impinj Octane SDK Example, 'ReaderEvents'. There is also an example of using a GPI trigger with the Impinj Octane SDK in the example called 'ReadTagsGpiTrigger'. 

 
Example - Using LLRP Example with R700 GPIO 

Another way to control the reader's GPIO is through using Low Level Reader Protocol (LLRP) programming, as shown in the code sample below.

 

private void GPO1_ON()
{
    // this routine turns on 3.3v power in LLRP GPO1
    // LLRP GPO1 = Hardware PIN 14 / GPOUT0MSG_SET_READER_CONFIG 

    msg = new MSG_SET_READER_CONFIG();

    msg.GPOWriteData = new PARAM_GPOWriteData[1];
    msg.GPOWriteData[0] = new PARAM_GPOWriteData();
    msg.GPOWriteData[0].GPOData = true;
    msg.GPOWriteData[0].GPOPortNumber = 1;
    MSG_SET_READER_CONFIG_RESPONSE rsp = reader.SET_READER_CONFIG(msg, out msg_err, 12000);
    if (rsp != null)
    {
        textBox2.Text = rsp.ToString();
    }
    else if (msg_err != null)
    {
        textBox2.Text = rsp.ToString();
    }
    else
       textBox2.Text = "Commmand time out!";
}
private void GPO1_OFF() { // this routine turns off power in LLRP GPO1 // LLRP GPO1 = Hardware PIN 14 / GPOUT0MSG_SET_READER_CONFIG msg = new MSG_SET_READER_CONFIG(); msg.GPOWriteData = new PARAM_GPOWriteData[1]; msg.GPOWriteData[0] = new PARAM_GPOWriteData(); msg.GPOWriteData[0].GPOData = false; msg.GPOWriteData[0].GPOPortNumber = 1; MSG_SET_READER_CONFIG_RESPONSE rsp = reader.SET_READER_CONFIG(msg, out msg_err, 12000); if (rsp != null) { textBox2.Text = rsp.ToString(); } else if (msg_err != null) { textBox2.Text = rsp.ToString(); } else
textBox2.Text = "Commmand time out!"; }

With the reader set to use the LLRP interface, you can also use the Impinj LTK and SDK libraries to configure the GPIO. This can be easily tested with the AdvancedGpo example, though it's important to make sure that you are only working with GPOs 1 through 3. In the example, it will include a configuration for GPO4, which is not offered on the R700, and will need to be commented out. This GPO4 configuration is included, as the Speedway Revolution Reader supports four GPOs, instead of the three supported with R700.

You  can also make use of the QueryFeatureSet() API call in the Octane SDK to determine how many GPOs are available for a specific reader. This way the code can be written to run safely on both a Speedway Revolution and an R700, if your use-case required this. An example of using this API call is shown in the 'QueryReaderSettings' example shipped with the Octane SDK.

It is also worth noting that GPO configuration is currently not supported with the Impinj IoT Device Interface, and can only be configured when using the Impinj LLRP Interface

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