elm337 elm electronics ?circuits for the hobbyist < http://www.elmelectronics.com/ > connection diagram pdip and soic (top view) v dd v ss 1 2 3 4 8 7 6 5 light switch the elm337 provides a convenient means to interface standard photocells or light dependent resistors (ldrs) to digital logic circuits. it provides an input comparator with hysteresis, line frequency filtering, digital delays, and high current output drivers all within the one 8 pin package. three mode setting pins configure the elm337 for pulse or continuous output and for a delay on change of from 1 msec to 10 minutes. the transition threshold is set with a single external resistor, simplifying designs and minimizing costs. applications need not be limited to those employing photocells, as the example applications section shows. the schmitt trigger input provides a convenient way to interface to virtually any input signal, whether from digital logic or from a slowly varying analog source. the remainder of the elm337 can simply be thought of as a time delay on pickup and dropout type circuit - very useful for sequencing processes. low power cmos design - typically 1ma at 5v operates from 3v to 5.5v no external timing elements required low parts count digitally selected delays of up to 10 minutes pulsed or continuous outputs internal line frequency filtering high current drive outputs - up to 25 ma automatic lighting controls security light beam monitoring position sensing light controlled counters time delay circuits ldr dark light m2 description applications block diagram 1 of 4 features elm337dsa m0 m1
elm337 elm electronics ?circuits for the hobbyist < http://www.elmelectronics.com/ > pin descriptions ordering information these integrated circuits are available in either the 300 mil plastic dip format, or in the 200 mil soic surface mount type of package. to order, add the appropriate suffix to the part number: 300 mil plastic dip............................... elm337p 200 mil soic..................................... ELM337SM 2 of 4 all rights reserved. copyright ?000 elm electronics. every effort is made to verify the accuracy of information provided in this document, but no representation or warranty can be given and no liability assumed by elm electronics with respect to the accuracy and/or use of any products or information described in this document. elm electronics will not be responsible for any patent infringements arising from the use of these products or information, and does not authorize or warrant the use of any elm electronics product in life support devices and/or systems. elm electronics reserves the right to make changes to the device(s) described in this document in order to improve reliability, function, or design. v dd (pin 1) this pin is the positive supply pin, and should always be the most positive point in the circuit. internal circuitry connected to this pin is used to provide power on reset of the microprocessor, so an external reset signal is not required. refer to the electrical characteristics section for further information. m2 (pin 2), m1 (pin 3) and m0 (pin 4) the digital levels at these pins determine the mode of operation, as shown in table 1 below. levels are read whenever the ldr input signal changes, so that modes can be changed ?n the fly? ldr (pin 5) this is the voltage sensing input pin. it uses schmitt trigger circuitry, and a peak detecting circuit for line frequency filtering so that slowly varying and pulsating signals will not cause circuit instability. a logic low level on this pin will be interpreted as the presence of light, while a logic high results in a dark input. see the example applications section for typical connections. dark (pin 6) and light (pin 7) these are the two active high circuit outputs. depending on the mode selected, they will either remain continually active, or provide a 50 msec pulse output on change from light to dark (dark output) or dark to light (light output). v ss (pin 8) circuit common is connected to this pin. this is the most negative point in the circuit. elm337dsa table 1. modes of operation mode inputs delay on transition to m1 l l h h l h l h m2 l l l l h h h h dark 50 msec 1 msec 50 msec 50 msec 10 sec 10 sec 10 min 10 min m0 l h l h l h l h type of output pulse continuous continuous continuous pulse continuous pulse continuous light 50 msec 1 msec 50 msec 50 msec 10 sec 10 sec 10 min 10 min
elm electronics ?circuits for the hobbyist < http://www.elmelectronics.com/ > elm337 electrical characteristics absolute maximum ratings storage temperature....................... -65? to +150? ambient temperature with power applied.................................... -40? to +85? voltage on v dd with respect to v ss ............ 0 to +7.5v voltage on any other pin with respect to v ss ........................... -0.6v to (v dd + 0.6v) note: stresses beyond those listed here will likely damage the device. these values are given as a design guideline only. the ability to operate to these levels is neither inferred nor recommended. 3 of 4 all values are for operation at 25? and a 5v supply, unless otherwise noted. for further information, refer to note 1 below. characteristic minimum typical maximum conditions units supply voltage, v dd 3.0 5.0 5.5 v v dd rate of rise 0.05 v/ms average supply current, i dd 1.0 2.4 ma notes: 1. this integrated circuit is produced with a microchip technology inc.? pic12c5xx as the core embedded microcontroller. for further device specifications, and possibly clarification of those given, please refer to the appropriate microchip documentation. 2. this spec must be met in order to ensure that a correct power on reset occurs. it is quite easily achieved using most common types of supplies, but may be violated if one uses a slowly varying supply voltage, as may be obtained through direct connection to solar cells, or some charge pump circuits. 3. as with all of the delays, the pulse timing is generated internally, and is affected by both temperature and supply voltage. variations are generally less than 5% of this value over the operating range. input low voltage v ss 0.15 v dd v input high voltage v dd v 0.85 v dd output low voltage 0.6 v output high voltage v v dd - 0.7 current (sink) = 8.7ma current (source) = 5.4ma see note 2 elm337dsa output pulse width 50 msec ldr input threshold voltages 2.8 v see note 3 4.25 v 1.3 to dark to light 0.75 0.85 v dd mode pins mode pins
example applications 4 of 4 figure 1 at right shows the elm337 installed in a typical lighting control circuit. the mode has been set to 111 (or hhh), resulting in delays of 10 minutes when recognizing a light or dark condition. in this case, only the ?ark?output (pin 6) is used to enable (and disable) a lighting circuit, but other variations on this theme might use the light output (pin 7), or possibly use mode 110 to provide short (50 msec) output pulses to trigger other circuits. the threshold setting resistor (22k w in figure 1) is chosen depending on what resistance it is desired to have the transitions to light or dark occur at. using the typical schmitt voltage thresholds for a 5 volt supply, it can be shown that the two resistances that switching will occur at are 1.33r t (light to dark) and 0.37r t (dark to light), where r t is the threshold setting resistance. for the 22k w shown, these would be at about 30k w and 8k w , respectively. the values that you choose would depend on the ldr used, and your application. if the ldr (r l ) is mounted more than a few feet from the elm337, the increased exposure could cause problems due to induced voltages and currents. to provide protection from these, a resistor (r prot ) should be added in series with pin 5 as shown at right. typically this resistor would be equal in value to the threshold setting resistor. elm337 elm337dsa elm electronics ?circuits for the hobbyist < http://www.elmelectronics.com/ > figure 1. yard lighting controller figure 2. time delay dropout switch the elm337 is also capable of operating simply as a delay circuit. by hard-wiring the mode pins for a desired delay, and applying logic levels to the ldr pin, symmetrical output delays of up to 10 minutes can be obtained. asymmetrical delays can also be obtained as shown in figure 2. this circuit connects the elm337 to provide a 50msec delay on pickup and 10 second time delay on dropout function. operation of the circuit can best be explained as follows. when the ?tart?pushbutton is pressed, the m2 and m1 pins will both be at a logic low level, while m0 will be high. the ldr input is also at a low level, simulating an ldr that is just ?eeing?light. since the mode is 001 or llh, then from table 1 (on page 2) the light output will go to a high level after 50msec. this delay is desirable as it ensures that the input is legitimate by providing some degree of switch debouncing. as soon as the pushbutton is released, the m2 mode pin returns to a high level, and what appears to be a dark input will be on the ldr pin. from table 1, with mode 101, the output will turn off after 10 seconds. certainly several other variations are possible by connecting the mode pins in different combinations. why not try your hand at some 0.01? to the controlled circuit 1 2 3 4 8 7 6 5 start 337 +5v +5v 22k w 22k w 1 2 3 4 8 7 6 5 +5v 0.01?
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