resistors provide the output with the high-state voltage when the phototransistor is off. in a phototransistor, base current is supplied when light strikes the detector, which effectively grounds the output. typically, the detector is operated in saturation. this means suffcient light is provided to completely sink, or ground, all the current provided by the pull up resistor plus that of the interfacing electronics. in the logic high state, the light is suffciently blocked by the rotor and the detector functions like an open circuit. the pull up resistor then provides sourcing current to the interfacing electronics. this on or off digital arrangement allows the open collec - tor to interface with popular integrated circuit technologies such as ttl, ttl ls, cmos, and hcmos. schmitt triggers to provide signal enhancement it is recommended that a schmitt trigger be con - nected to each output. this device is already included in the series 61k, 61r, 63k and 63r encoders. the schmitt trigger cleans up the output into a pure digital signal. it does this by removing the small linear region between the on and off states of the detector. dur - ing this transition the light is only partially blocked and the output is somewhere be - tween what the interfacing circuit might con - sider to be on or off. in other words, the output is not completely digital. the schmitt trigger contains a very important feature which makes it attractive for this application. the device has a higher threshold, or trigger level, when it is in the on state than it does in the off state. this hysterisis flters any electrical noise, which can cause the output to change state rapidly during the transition. and since the output from the schmitt trigger is a pure digital signal and is isolated from the phototransistor, the signal is basically immune to loading problems that can effect encoders without the schmitt trigger. schmitt triggers are available in most popular ic technologies. shaft and panel seal a shaft and panel seal are available to provide water-tight mounting for the series 61b, 61d, 61k, 61r and 62 encoders. sealing is accomplished by an o-ring shaft seal and a panel seal washer. the panel seal washer in the 61b and 61d encoders does not affect the overall dimensions of the switches. in the 61k and 61r encoders, the .045" thick washer is placed over the threads and sits fat on the base of the bushing. the 61ks and 61rs are also epoxy-sealed on the bottom of the switch to provide a completely sealed switch. optical encoder engineering information quadrature all grayhill encoders use quadrature output code, which is the same as a 2-bit, repeating gray code. quadrature is the most popular and cost effective output format because only two detectors are required. however, quadrature can only be used in ap - plications where incremental data is required. absolute positioning is not possible because the code repeats every four positions. in other words, changes in the encoder in magnitude and direction can be determined, but the actual position of the encoder cannot. in most applications this is not a problem. in a quadrature rotary optical encoder two detectors are used to provide outputs, a and b. the code rotor either blocks the infrared light or allows it to pass to the detec - tors. as the shaft turns the rotor, the outputs change state to indicate position. the result - ing output is two square waves which are 90 out of phase. open collector output the open collector output is typical of the series 61b, 61c and 62, and is the sim - plest form of output available. the frst step in interfacing with open collector outputs is to provide an external pull-up resistor from each output to the power source. these pull-up open collector output schmitt trigger power source external pull-up resistor output phototransistor current flow high output level to next stage phototransistor as an open switch power source external pull-up resistor output phototransistor current flow low output level to next stage phototransistor as a closed switch upper threshold lower threshold input to schmitt trigger output from schmitt trigger output low output high output low light blocked light partially blocked light detected power source external pull-up resistor output phototransistor schmitt trigger www.grayhill.com
available from your local grayhill distributor. for prices and discounts, contact a local sales offce, an authorized local distributor or grayhill. series 65 optical encoder interface features ? interfaces with all grayhill and most standard quadrature optical encoders ? power reduction of up to 75-90% in optical encoder use through power management feature ? user selectable output modes: magnitude/direction, up/down, ordering information gh65c11-x-yy temperature: packaging: c = commercial (0 c to 70 c) pd = 18 lead 300 mil wide plastic dip n = industrial (-40 c to 85 c) so = 18 lead 300 mil wide gull wing soic ss* = 20 lead ssop * the ss package style is not available in the -40c to 85c temperature range. ? standard quadrature ? simplifed microprocessor interface reduces design time ? debounces encoder integral pushbutton switch ? ideal for battery powered applica - tions that include optical encoders description the gh65c11-x is designed to receive input from standard quadrature optical encod - ers. the power management feature allows power to the encoder to be applied only dur - ing sampling intervals, thus conserving power (especially advantageous in battery powered systems). sample rate is a nominal 4k per second allowing high speed quadrature input. the optical encoder interface can operate in 1 of 3 user-selectable output modes. these modes are: magnitude and direction, up and down count, and standard quadrature. debouncing of an integral pushbutton switch within the optical encoder can also be ac - complished. name type* description m0, m1 i mode selection input pins v dd p 3C6 vdc power source res i reset pin, normally connected to v dd v ss p gnd, 0v nominal power return ?ai, ?bi i phase a and b quadrature input pins swi i switch input pin swo o debounced switch output pin nc o no connect, this pin must be left unconnected pw o power source for encoder power management rc i/o rc oscillator pin ?bo/dn/dr o phase b, down, direction, mode conditional output pin ?ao/up/mg o phase a, up, magnitude, mode conditional output pin * pin types: i = input, o = output, p = power. m0 m1 v res v ?ai ?bi swi swo ?bo/dn/dr ?ao/up/mg rc nc v pw pw pw pw soic/dip dd ss dd 1 2 3 4 5 6 7 8 9 18 17 16 15 14 13 12 11 10 m0 m1 v res v v ?ai ?bi swi swo ?bo/dn/dr ?ao/up/mg rc nc v v pw pw pw pw ssop dd ss ss dd dd 1 2 3 4 5 6 7 8 9 10 20 19 18 17 16 15 14 13 12 11 bulletin 1223 rev 04/14 www.grayhill.com
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