Digital Contacting Rotary Encoder
Also called a Bit Switch, Grey switch or Digital Switch, rotary encoders provide 8 bits of digital Grey-coded signals that allow an microcontroller to determine position of a shaft. The advantage of the encoder is that it permits the direct entry of digitised analog data into a digital circuit without A/D conversion
The absolute contacting encoder is an absolute position input device. It is an absolute encoder implemented in a contacting technology. The special feature is that they assign a unique, digitally encoded signal to each measured increment which prevents erroneous readings. For example, if a power failure or transient malfunction occurs, the position can be read when the power is restored without moving back to a reference position, as would be required with an incremental encoder. The absolute digital output simplifies the electronic circuit by allowing the microprocessor to be directly linked to the ACE™ encoder. Because the ACE™ encoder offers a unique absolute output from a single track, the resulting lower sample rate requires much less microprocessor time, resulting in lower overall power consumption. Output: 8-bit gray code with 128 absolute states. Closed Circuit Resistance: 5 ohms max. Electrical Travel and Mechanical Angle: Continuous. Contact Bounce (60 RPM): 2.7 ms max. RPM (Operating): 120 max. Weight: Approx. 0.5 oz.
Figure : Picture of the Bourns EAW rotary encoder from
•Contact rating: 10 milliamps at 10 VDC
•8 – bit gray code with 128 absolute states and 256 bytes of codes
•Operating temperature: 1degree C to 85 degree C
•Can handle 15 G of vibration and 50 G of shock
Advantage:
•Keeps position when power is out or transient malfunction
•Cheap
•offers a unique absolute output from a single track, the resulting lower sample rate requires much less microprocessor time, resulting in lower overall power consumption
•It is contacting which wear out unlike optical encoders but hasrotational life: 50K shaft revolutions. If each day the door is operated 10 times a day, at half revolution each time, it’s about 5 revolutions per day, which gives about 10000 days.
•Can discard unwanted bits to reduce information
Table: Pin output code for encoder. 1 denotes an open switch and 0 denotes a close switch
It has a full rotation of 360 degrees and has 128 states so it is about 2.81 degrees per state. Our door needs to be opened up to about 105 degrees so we need 37 states difference between opening and closing. We can pick any state to be the opening and any other state to be closing. Set 3 states as close and set 3 states as open to count for the any off set for the encoder. The diameter of the bore hole is 6.32mm or .25 inches. The bore hole of the main axle is about .5 inches diameter. The Tsubaki sprocket is chosen for the main axle with 9 teeths and size 40. The Poly Hi Solidur sprocket is chosen for encoder, which is size 25, and 9 teeths.
Flow chart: Opening and closing process of the door.
Test case: Accompany the flowchart.
AWG / Diameter / Turns of wire / Area / Current Rating / Max Current Rating(mm) / (per cm) / (mm²) / (A) / (A)
6 / 4.115 / 2.43 / 13.3 / 37 / 101
7 / 3.665 / 2.73 / 10.5 / 30 / 89
8 / 3.264 / 3.06 / 8.37 / 24 / 73
9 / 2.906 / 3.44 / 6.63 / 19 / 64
10 / 2.588 / 3.86 / 5.26 / 15 / 55
11 / 2.305 / 4.34 / 4.17 / 12 / 47
12 / 2.053 / 4.87 / 3.31 / 9.3 / 41
13 / 1.828 / 5.47 / 2.62 / 7.4 / 35
14 / 1.628 / 6.14 / 2.08 / 5.9 / 32
15 / 1.45 / 6.89 / 1.65 / 4.7 / 28
16 / 1.291 / 7.75 / 1.31 / 3.7 / 22
Table E.1.1: Wire Gauge Current Specifications(NEC Standards 2005)
16 gauge wires might be able to be found in RIT or mouser part number 538-19144-0039
To protect the user from electrical shock, the power board will be placed in a protective case. The enclosure will be electrically isolated from the power board and will have external connectors mounted to its end caps. These will allow the user to plug in the battery and external modules into the power board without having to open the case.