072-0500
Alphasense User Manual
OPC-R1 Optical Particle Counter
Issue 1
Alphasense Ltd
Page 6 of 33
February 2019
Sensor Technology House, 300 Avenue West, Skyline 120, Great Notley. Essex.CM77 7AA. UK
Tel: +44 (0) 1376 556700 - Fax: +44 (0) 1376 335899
Email: [email protected] - Web: www.alphasense.com
particle flow. Coarse gauze filters can also be used to prevent the ingress of large particles or
insects without interfering with the fine particles being measured. All electrical connections must be
protected from moisture and temperatures outside of the operational range.
The temperature and humidity sensor is mounted on the OPC-R1 PCB. The values reported may
not represent the actual ambient conditions.
Connecting and Operating The OPC R1
7
Connecting power and taking readings
The OPC-R1 is shipped pre-calibrated. There are no user serviceable parts. Power and data
communications are provided via the SPI socket. Firmware updates use the SPI connector.
Connection to the OPC-R1 for real-time data transfer can be made via the SPI direct to your own
circuit
’s internal bus using your own or the SPI interface provided by Alphasense. The SPI interface
supplied by Alphasense requires a USB A-B lead to connect to the USB port of a computer, this
must be ordered separately. The green LED shows that power is supplied to the OPC-R1 and the
red LED flashes when the PC and OPC-R1 are communicating.
SPI Connection
The SPI socket is a Molex 'Pico Clasp' 6 way Housing, Part Number 501330-0600. Pins are
assigned in table 2.
Pin
Function
1
Vcc
2
SCK
3
SDO
4
SDI
5
/SS
6
GND
Table 2. SPI pin assignments
OPC power requirement
The OPC-R1 requires a 4.8 to 5.2 Volt DC supply with minimum electrical noise, (< 30mV pk-pk)
This is stepped down to a 3v3 supply (via the SPI-ISS adapter) for the SPI logic lines. Except for the
Slave-Select logic line, the SPI interface lines are 5V tolerant but we recommend to run all at 3v3.
The OPC-R1 requires 95-100 mA with a short one amp transient at switch-on, check that the current
limit is not exceeded if multiple units are operated from a shared power supply
It is recommended to allow 2 second for the OPC to respond to the first SPI command after power-
up and >0.6 s after a switch peripherals/fan on sequence.
Software interface configuration
The following interface rules will help you to make a reliable connection with the OPC.
1.
Set up SPI interface as follows:
SPI Mode1 (clock idle low, data transmitted on clock leading edge).
Set SPI frequency to between 300 kHz and 750 kHz.
2.
SPI Master system must drive MOSI and SCK and SS communication lines.
3.
Delay between a command byte and any subsequent bytes of an SPI communication should
be > 10 ms (< 100 ms).
