HydraFerret: Multi-sensor IOT with a simple interface.
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This device acts as a high speed counter (up to 1MHz) with a maximum count of 1,000,000. In theory this should permit the counter to be used with an ultrasonic sonar to give millimeter perfect distance readings. However, in practice some variation will be observed, and some sonar devices may be more consistent than others.
there are a number of different sonar designs that can be used with Hydraferret, all using the same principle of operation. This is true for units with separate transmit and receive sensors or a combined one or weather proof ones. If installing into a damp (or potentially damp/humid) environment be sure to select a sonar with sufficient weather proofing.
Measuring distance using the pfc8583 counter works as follows:
In many Arduino distance measurement sketches the processor clock cycles are counted for the duration the "echo" output is high and this is multiplied by an approximate speed of sound. This approach has not been taken for the HyraFerret project for the following reasons:
The minimum configuration is to simply added the sensor and restart the esp32. The configuration of the I2C bus is discussed elsewhere on this page. Each pfc8583 should have unique address on the bus on which it is located. The pfc8583 devices are numbered 0 to 4, starting with units on bus 0 then bus 1. On each bus the number allocation is in device address sequence.
When using for distance measurement a maximum oscillator frquency supported by the pfc8583 is 1MHz. A logical AND can be done using one part of a CMOS 4081, or half 4011 or using 2 diodes and pull up resistor. When using a diode AND, the cathodes (negative side) face the osciillator and echo outputs. The anode (positive sides) are tied together and have a pull up resistor. The anodes then provide the ociillator input to the pfc8583. If using a CMOS device as an AND gate, tie any unused inputs to ground.
An oscillator chip such as MCO-1510A can be used to give an accurate pulse source. This oscillator is a 4 pin device in a 14 pin DIP package profile and has ground connection to pin 7, output pin 8, and 5V to pin 14.
critical|extreme|warning pfc8583 <0-1> var disable critical|extreme|warning pfc8583 <0-1> var <rpn-expression> enable or disable alerting thresholds on sensors devicename pfc8583 <0-1> <device-name> Name a sensor device [enable|disable] [showlogic] Enable or disable display of rpn logic for alerts frequency [pfc8583 <n> <frequency>] Set reference frequency in Hz for time dependant measurement Use frequency of 1 for counter, and 0 for non-resetting counter eg if using 1MHz osc for distance measurement, frequency will be 1000000 i2c [<0-1> <sda> <scl> [speed]] Set i2c pins, eg: 21 and 22 for bus-0, and 5 and 4 for bus-1 interval pfc8583 <1-300> Set the interval between measurements taken by the sensor. remove pfc8583 Remove all discovered pfc8583 devices from monitoring cycle NB: Removal does not persist after reboot. rescan pfc8583 Rescan i2c busses for added or removed devices of specified type. transform [pfc8583 <n> <rpn-formula>] The transform formula is applied to the "xfrm" variable each measurement interval transformname [pfc8583 <n> <name>] Apply the name to a transformation trigger [pfc8583 <n> <pin>>] Use the specified pin to generate a short trigger pulse at the start of pfc8583 measurement Typically used for start of ultra-sonic measurements rpn variables: pfc8583.dev - count of pfc8583 sensors (DEVice count) pfc8583.freq - frequency of oscillator to use for distance calculation pfc8583.pin - Trigger pin number pfc8583.coun - Count as a the last 5 minute interval pfc8583.lasc - Last count pfc8583.dist - Average measured distance in cm over 5 minute period pfc8583.lasd - Last measured distance in cm pfc8583.xfrm - result of transform calculation (if defined) pfc8583.csta - 0=OK, 1=warn, 2=critical or 3=extreme status
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