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Registered Member #14
Joined: Thu Feb 02 2006, 01:04PM
Location: Prato/italy
Posts: 383
I managed to obtain few samples of the Ad5040 rotary encoder from Austria Microsystems. I set up a small PCB board to house the ic and a few resistors, 2 leds, and some decoupling capacitors (Important!) to test it using two multimeters one for PWM output ( 0-5V corresponding to 0-360°) and one for the pulse output (256 pulses per revolution, plus one additional quadrature channel) and an analog oscilloscope to see the waveforms. I'm very surprised about the accuracy and tolerance to vibration and magnet misalighnment, also i used a cubic magnet instead of a cylincrical one. I'm planning to use two of them for the new version of the wind logger, adding a channel for the wind vane using those chips as sensors. One chip will be used for the wind vane sampling the PWM (filtered) output ad DC voltage with the onboard PIC-adc, the other will be used for speed measurement sampling the 256 pulses-per-revolution with the PIC-onboard counter. The wind speed resolution will increase from 0,5 Km/h (sampling time 1s) to 0,1 km/h (sampling time 0,5s). The drawback of those chips is power consumption, that is about 15-18 mA per chip.
Registered Member #14
Joined: Thu Feb 02 2006, 01:04PM
Location: Prato/italy
Posts: 383
Update:
I constructed an anemometer sensor using a 4mm 1cm long radially polarized NdFeB (N45 grade) magnet and an AD5040 working in default mode (256 pulses per revolution, quadrature A-B). The cups of the anemometer ar coupled to a rotating shaft where the magnet is housed (inside a PVC tube). The circuit is kept ad a distance of 2mm from the rotating magnet and is totally waterproof. The 256 pulses per revolution give an insane resolution (0.05 Kmh) way below the accuracy of the mechanical part. Alignment is simple observing the magnetic fault outputs (pulled low if the magnetic field configuration is invalid). Bigger radially polarized magnets interact too strongly with the earth magnetic field but the 4mm one minimizes this effect. The windvane works on the same principle listening to the PWM output instead of the incremental one giving a filtered voltage from 0 to 5V proportional to the angle. The bearing was a rollerblade bearing sonicated in DichloroMethane (to remove the grease) and oiled with firearm grade spray oil. Questions?
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Experiments with the AD5040
