GLOLABWireless Control

1

Introduction______________This project was published in the April 1999issue of Popular Electronics magazine.

Today wireless is used almost everywherefor almost everything. Devices are availableto send audio, video, security data,computer data, to open garage doors andturn on lights. However, for a specificcontrol or pulse application not covered byone of these available devices you usuallyhave to build your own. In the past, buildinga simple and reliable RF transmitter andsensitive receiver was not easy. And afterbuilding them some difficult adjustmentsand measurements would have to be madeto set operating frequency, minimizeharmonic radiation and maximizesensitivity.

But now, thanks to new transmitter andreceiver modules from Linx Technologies,all of those problems are things of the past.You simply apply power to the transmitterwhich is SAW (Surface Acoustic Wave)based for accurate frequency control andattach an 6.7 inch whip antenna to senddata. The same is done for the receiverwhich is a SAW based superhetrodynehaving excellent stability and sensitivity.Absolutely no adjustments of any kind arerequired. The modules operate at 418 Mhzwith a range of better than 300 feet. ThisWIRELESS CONTROL project uses thesemodules to send and receive control signalsthat can be used for a variety of purposes.

Most wireless devices that are not dedicatedto, or a part of a video, audio or computersystem simply indicate the pressing of apush button or closing of a switch. But theWIRELESS CONTROL transmitter circuitswill accept inputs from switches, electronicdevices such as photo transistors,microprocessors, computers and otherdevices that produce conduction or voltagelevels. It will send data indicating both theclosing and opening of a switch, both theconduction and turn off of an electronicdevice and both the rise and fall of an inputvoltage. The receiver has threecomplementary outputs that cover almostany application. One is momentary, anotherlatched and another sequential. You are nolonger bound by those push button devicesthat were the only thing available until now!

How it works______________

TransmitterFigure 1 is a schematic of the transmitter.IC1 is a Maxim MAX934 quad micropowercomparator with a built in voltage reference.C1 filters any RF that may enter the inputfrom the antenna. IC1A receives an inputthrough R3 which adds isolation allowing theinput to accept high overdrive voltageswithout damage. Electrostatic dischargeprotection diodes built into the MAX934inputs are rated at 20ma and can easilyclamp the overdrive from R3. Hysteresisfeedback through R4 adds switch debounceand noise immunity. R2 is a 1.6microampere current source that pulls theinput to an up level turning IC1A on. Theinput is very sensitive because of this lowpull up current and can be pulled downbelow the switching threshold by an inputdevice having an impedance of about 1megohm. It can be pulled down by closing aswitch, by a photocell, a water detector orby other sensing elements. An externalvoltage can also be applied to the input toswitch it on and off. The switching thresholdis approximately equal to the internalreference voltage of 1.2 volts. One end of100 Kohm resistor R1 is brought out to a

GLOLABWireless Control

2

bias terminal so it can be connected to theinput through an external potentiometer orresistor to provide sensitivity and thresholdadjustment when used with a photocell orsimilar device. The maximum currentavailable from the bias terminal is 50microamperes.

IC1B inverts the output of IC1A making bothphases of the input signal available. Apositive transition from IC1A will couplethrough C2 and D1 into IC1C and a positivetransition from IC1B will couple through C3and D2 also into IC1C, therefore, wheneverthe input goes either up or down, a positivepulse is coupled into IC1C. The timeconstants of either C2 and R5 or C3 and R5turn IC1C on for about 2 seconds as C2 orC3 discharges. D3 recharges C2 and D4recharges C3 during negative transitions.R6 and R7 add hysteresis feedback to IC1Cfor stability during the slow discharge of C2and C3. The output of IC1C triggers thetransmit module on for about 2 secondsthrough inverter IC1D and Holtek HT680encoder IC2. Upon being triggered by IC1D,the encoder generates three groups of bitscontaining data and address informationand serially sends them to the transmitmodule. These three groups are repeatedlytransmitted during the 2 second duration ofthe trigger pulse. Both phases of the inputsignal are also sent to data pins 3 and 4 ofthe encoder to transmit unique codes for aninput opening and closing.

The encoder can be programmed by 4position DIP switch SA for 16 differentaddresses so that more than one pair oftransmitters and receivers can be used inclose proximity without interference. Thecircuits are powered with 5 volts throughreverse polarity protection diode D5 andTelcom TC55RP5002EZB low dropoutmicropower regulator IC3 by a 6 or 9 voltbattery.

ReceiverFigure 2 is a schematic of the receiver. Theoutput from the receive module feedsthrough level shift diode D6 into HoltekHT692 decoder IC4 which can be

programmed by DIP switch SB for 16different addresses to match the transmitter.The decoder sequentially receives the threegroups of bits containing data and addressinformation, stores them and comparesthem with each other. If two of them match,the decoder data output pins 3 or 4,depending on the transmitter input, go to anup level and remain there as long as a validdata stream is being received. This codingtechnique ensures that only valid data willget through and random noise pulses will berejected.

The two outputs from the decoder pins 3and 4 that correspond to the encoded datain the transmitter are fed into a TelcomTC4427 dual, level translating power driverIC5 and into CD4013 flip flops IC6A andIC6B.

IC5A and IC5B supply complementary 12volt momentary pulses at up to 200masource or sink to whatever loads you maywant to drive. A set-reset push button andthree, status LEDs are mounted on theboard for easy testing. LED1 is a dual colorLED that shows momentary data beingreceived.

Flip flop IC6A can be programmed by SC tobe both set and reset by the decoderoutputs or to be set by one of the outputsand reset by push button SD. It can also bereset by one of the outputs and set by SD.The latched outputs of IC6A feed into powerdriver IC7 that provides complementary 12volts at 200 ma source or sink. LED2indicates the state of IC6A.

Flip flop IC6B is triggered by the decoderoutput that represents a transmitter inputgoing down. It will alternately flip each timethe input goes down. The latched outputs ofIC6B feed into power driver IC8 that alsoprovides complementary 12 volts at 200masource or sink. LED3 indicates the state ofIC6B.

The receive module, IC4 and IC6 arepowered by 5 volts through regulator IC10while IC5, IC7 and IC8 are powered by 12volts through regulator IC9 from DC walltransformer T1.

GLOLABWireless Control

3

The six outputs give great flexibility in thetype of loads that you can drive. Themomentary outputs from IC5 at terminals 1and 2 will give a short beep if a piezobuzzer is used. It can indicate a transmitterinput closing or opening, or both if twobuzzers are used with different tones. Theoutputs from IC7 at terminals 3 and 4 willlatch in different states and thus exactlycorrespond to an input closing and openingor it can be programmed to latch on closingonly or opening only and be manually set orreset by SD. This is useful to store theresults of temporary event such as amailbox door being opened by the postman.The outputs from IC8 at terminals 5 and 6can be used to sequentially turn a lamp onand off through a relay each time a contactis closed at the transmitter. Since the powerdrivers supply 12 volts and can source orsink 200ma continuous and more than 1amp peak, many different types of loadscan be driven either directly or throughmechanical or solid state relays.

Construction______________

BoardsBecause the transmit and receive modulesare of the surface mount type they arealready mounted on PC boards. Both of theboards are double sided to provide a goodground plane for the modules and to keepall components on the same side of theboard.

Sockets are used for all of the DIP ICs. Toassemble the boards mount all of the smallcomponents first, then add the sockets andterminal blocks. Connections for a remoteset-reset button at terminals 7 and 8 and alloutputs are available on the terminal block.Mount the LEDs with the long lead on thebottom when the board is viewed from thecomponent side with the receive module atthe top. After all components are mountedsolder the leads from a 9 volt batteryconnector or from a four or six cell holder tothe transmitter board holes marked plus v

and minus v. Connect and solder the walltransformer leads to the holes marked plusand minus on the receive circuit board nearIC9. Connect the positive lead with thewhite tracer to plus hole. The boards maybe installed in enclosures of your choice orused without enclosures. Mounting holes for2-56 screws are provided in the corners ofeach board. If an enclosure is used for thereceiver, a set-reset button and one or moreLEDs may be mounted in the enclosurepanel for easier button access and LEDviewing. The antennas are stiff pieces ofwire 6.7 inches long connected to theantenna terminals. The transmitter ispowered by a 9 volt battery or four to six AAor AAA cells. The larger number of cells willextend battery life by providing a reservevoltage above that which is required.

TestingConnect a 9 volt battery or four to six 1.5volt cells to the transmitter. Plug thereceiver wall transformer into a receptacle.Set switches SA in the transmitter and SB inthe receiver for all positions OFF, all ON oranywhere in between. However you setthem, they must be the same in eachtransmitter - receiver pair. Connect atemporary SPST test switch from thetransmitter input to ground.

Set SC1, SC2 ON and SC3, SC4 OFF.LED1 should not be lit. Both LED2 andLED3 should be either red or green. Closethe input switch and LED1 shouldmomentarily light red (blink) for two secondsand then turn off, LED2 should light red andremain lit and LED3 should change color.Open the input switch and LED1 shouldblink green, LED2 should light green andremain lit and LED3 should remain as itwas.

Set SC1 OFF, SC2 ON, SC3 ON and SC4OFF. Press SD to change LED2 to green ifit is not already green. Close the inputswitch and LED1 should blink red, LED2should light red and remain lit and LED3should change color. Open the input switchand LED1 should blink green, LED2 shouldremain red and LED3 should not change.

GLOLABWireless Control

4

Press push button SD and LED2 shouldchange to green.

Set SC1 ON SC2 OFF, SC3 OFF and SC4ON. Press SD to change LED2 to red if it isnot already red. Close the input switch andLED1 should blink red, LED2 should remainred and LED3 should change color. Openthe input switch and LED1 should blinkgreen, LED2 should change to green andLED3 should not change. Press SD andLED2 should change to red.

Repeat each of the above tests a few timesafter changing the SC switch settings assome toggling of the latch may occur duringthe setting of the switches.

Table 1 shows SC switch settings for inputand output conditions.

NOTE: The transmitter and receivermodules used in these kits are not certifiedby the Federal CommunicationsCommission. Assembled kits cannot be soldas a product without being FCC certified.The kits are intended for personal orexperimental use.

ANTENNA

+5SA

123456789

10 11 12 13 14 15 16 17 18

5

2

7 1

R1100K

R23M

R3

240K

R4

10M

C2 .1

C3 .1

D1

D2

D3 R510M

D4

D3

R6

R7

10M REF

REF

REFREF

4

5

2

6

7

1

13

12

15

11

10

16

PIN 3 = +5PIN 14 = GNDPIN 8 = REF

IC2

IC1A IC1B IC1C IC1D

+5

IC1

WIRELESS CONTROL TRANSMITTER FIGURE 1

R8390K

BIAS

IN

GND

+

+ + +

___

_

100K

+5

C4 C5

.1100

6 - 9 VOLTS

1,2,3,4

IC3

+

D5

TRANSMITMODULE

GLOLABWireless Control

Glolab Corporation134 Van VoorhisWappingers Falls, NY 12590

http://www.glolab.comemail kits@glolab.comfax (914) 297-9772

c 1999

+

C1

.01

ANTENNA

+5SB

123456789

10 11 12 13 14 15 16 17 18

PIN 14 = +5PIN 7 = GND

IC5, IC7, IC8

IC4

IC6

WIRELESS CONTROL RECEIVER FIGURE 2

R9390K

SC2

SC4

SD

R111M

R101M

+5

1

6

3

5

6

4

3

5

11

9

10

8

13

12

1

2

PIN 6 = +12PIN 3= GND

RECEIVEMODULE

120

VACT1

C6

1000

C8

.1

C7

.1

+5

+12

IC10

12

VDC

MOMENTARY

SEQUENTIAL

IC6A

IC6B

SC1

SC3

C9

100

IC9

1,2,3,4

0

2

1

4

3

7

8

RESET

Glolab Corporation134 Van VoorhisWappingers Falls, NY 12590

http://www.glolab.comemail kits@glolab.comfax (914) 297-9772

GLOLABWireless Control

c 1999

+

+

2

4

7

5

R12 .47K

LED1

A

B

IC5A

IC5B

R G

LATCHING

2

4

7

5

R13 .47K

LED2

A

B

IC7A

IC7B

RG

2

4

7

5

R14 .47K

LED3

A

B

IC8A

IC8B

RG

6

5

+5R15

100K

D6

GlolabWireless Control

XMIT SC SWITCH SETTINGS TERMINAL BLOCK NUMBERSINPUT SC1 SC2 SC3 SC4 1 * 2 * 3 4 5 6CLOSED ON ON OFF OFF R R TOG TOGOPEN ON ON OFF OFF G G NC NCCLOSED OFF ON ON OFF R R ** TOG TOGOPEN OFF ON ON OFF G NC NC NC NCCLOSED ON OFF OFF ON R NC NC TOG TOGOPEN ON OFF OFF ON G G ** NC NC

CLOSED = Transmitter input at a down levelOPEN = Transmitter input at an up levelR, G = Red or Green LED indicates a terminal at an up level* = Momentary - terminal at up level for two seconds** = Can be reset to opposite color by pressing SDTOG = Toggles to opposite colorNC = No change

TABLE 1

Parts List GlolabWireless Control

Wireless Control Transmitter parts Wireless Control Receiver parts

R1, R7 - 100K 1/8 watt 5% R9 - 390K 1/8 watt 5%R2 - 3 MEG 1/8 watt 5% R10, R11 - 1 MEG 1/8 watt 5%R3 - 240K 1/8 watt 5% R12, R13, R14 - .47K 1/8 watt 5%R4, R5, R6 - 10 MEG 1/8 watt 5% R15 - 100K 1/8 watt 5%R8 - 390K 1/8 watt 5% C6 - 1000 MFD 25 volt electrolyticC1 - .01 MFD 100 volt polyester film C7, C9 - .1 MFD 50 volt metalized filmC2, C3, C5 - .1 MFD 50 volt metalized film C8 - 100 MFD 10 volt electrolyticC4 - 100 MFD 10 volt low leakage electrolytic D6 - 1N914 diodeD1, D2, D3, D4, D5 - 1N914 diode LED1, LED2, LED3 - red-green dual-colorSA - 4 position DIP switch LED standoff - three3 position terminal block SB, SC - 4 position DIP switchIC socket 16 pin SD - momentary push button switchIC socket 18 pin 9 position terminal block (3 - 3 pos. blocks)IC1 - Maxim MAX934 micropower comparator IC sockets three 8 pinIC2 - Holtek HT680 encoder IC socket 14 pinIC3 - Telcom TC55RP5002EZB 5 volt regulator IC socket 18 pin9 volt battery connector IC4 - Holtek HT692 decoderAntenna terminal block IC5, IC7, IC8 - Telcom TC4427 power driver6.7 inch antenna wire IC6 - National CD4013 dual D flip flopCircuit board with transmit module IC9 - National 7812T 12 volt 1 amp regulator

IC10 - National 78L05 5 volt 100 ma regulatorT1 - 12 volt 200 MA DC wall transformerAntenna terminal block6.7 inch antenna wireCircuit board with receive module

1999Glolab Corporation http://www.glolab.com134 Van Voorhis email kits@glolab.comWappingers Falls, NY 12590 fax (914) 297-9772

Applications GLOLABWireless Control

1

The transmitter sends a unique digital codewhen the input goes from a down level to anup level and another unique digital codewhen the input goes from an up level to adown level. A down level is defined as anyvoltage lower than the threshold voltage of+1.2 volts down to -50 volts. An up level isdefined as any voltage higher than +1.2volts up to +50 volts. The input range islimited only by the voltage rating of C1.Since the transmitter sends information tothe receiver telling it both when the input isgoing up and when it is going down, it is notnecessary to be concerned about whetheryour input device is normally open ornormally closed. One of the many receiveroutput options can be chosen to give thedesired response.

The input terminals may be driven by TTLor CMOS levels from a computer,microprocessor or logic circuit as shown inFigure 1.

BIAS

IN

GND

INPUT FROM COMPUTER ORMICROPROCESSOR

Figure 1

A simple input device is the push buttonswitch shown in figure 2. When the switch isopen, the input is pulled up to 5 volts byinternal resistor R2. When it is closed, theinput is connected to ground.

BIAS

IN

GND

PUSHBUTTONSWITCH

Figure 2

Another switch is the magnetic reed infigure 3 which is activated by a magnetbeing placed close to it. This is good for noncontact applications such as placing theswitch on a window frame and the magneton the window so that the switch willactivate when the window is opened.Another useful application is to use theswitch to signal when the mail man opensthe mailbox door.

BIAS

IN

GND

MAGNETICREEDSWITCH

Figure 3

And yet another form of switch is thethermostat in figure 4. It can either close oropen in response to hot or cold and be usedto signal a below freezing condition or as aremote control for an air conditioner , oilburner or electric heater when used with theappropriate output configuration at thereceiver.

BIAS

IN

GND

THERMOSTAT

Figure 4

Figure 5 shows a water level detector thatcan be used to signal a leak in thebasement. The probes can be placed on thefloor near the water softner or heater tank.Probes can also be placed in soil near aplant to indicate when it should be watered.

Applications GLOLABWireless Control

2

BIAS

IN

GND

WATERLEVELDETECTOR

Figure 5

Figure 6 is also a water detector but is moresensitive because the detection area islarger. A piece of printed circuit board withinterleaved traces detects small quantitiesof water. This probe can be placed near awindow or patio door to signal rain entering.

BIAS

IN

GND

R1

SENSITIVEWATERDETECTOR

Figure 6

A resistive photocell of cadmium sulphide orother photo sensitive material connected tothe input as shown in figure 7 forms a verysimple light sensor. It can be used to signala basement or attic light left on or anemergency exit light failure. 10 mfdcapacitor C1 reduces 60 Hz pickup fromfluorescent lights.

IN

GND

RESISTIVEPHOTOCELL

+ C1

Figure 7

Figure 8 shows a similar photocell but withthe addition of a variable resistor connectedfrom the bias terminal to the input to varythe sensitivity of the photocell to light. Thisis useful to adjust for the amount of lightneeded to switch the circuit, such as whenusing it to sense daylight and turn a lampoff. The bias terminal will supply up to 50microamperes through its internal 100Kohm resistor.

BIAS

IN

GND

RESISTIVEPHOTOCELL

R1

C1+

Figure 8

Figure 9 is similar to figure 8 except a phototransistor is used in place of the resistivephotocell. It can be used as a robotproximity or direction sensor.

BIAS

IN

GND

PHOTOTRANSISTOR

R1

C1+

Figure 9

A single Light Emitting Diode may beconnected from any output pin to groundwith a series current limiting resistor asshown in figure10. Resistor R1 can be about470 ohms for a LED current of about 20milliamperes.

Applications GLOLABWireless Control

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GND

LIGHTEMITTINGDIODE

R1ANY OUTPUT

Figure 10

Figure 11 shows how to connect a threelead dual color LED to an output. The twoanode leads may be connected to anyoutput pins 1 and 2, 3 and 4, or 5 and 6.Current limiting resistor R1 can be about470 ohms for an LED current of about 20milliamperes.

R1

THREELEADLIGHTEMITTINGDIODE

ANY OUTPUT

ANY OUTPUT_______

GND

Figure 11

Figure 12 shows how to connect a two leaddual color LED. The polarity must bereversed to change color so you mustconnect to the two complementary outputsof an output pair such as pins 1 and 2, 3 and4 or 5 and 6. Current limiting resistor R1 canbe about 470 ohms for about a 20milliampere current.

R1TWOLEADLIGHTEMITTINGDIODE

ANY OUTPUT

ANY OUTPUT_______

Figure 12

A piezo buzzer may be connected from anyoutput to ground to produce an audiblealarm as shown in figure 13. The bestconnection is to a momentary output whichwill produce a two second beep whenever itis activated. You can connect two buzzerswith different tones to the twocomplementary momentary outputs tosignal a transmitter input going up anddown.

GND

MOMENTARY

PIEZOBUZZER

Figure 13

An opto coupler may be connected to anyoutput with a current limiting series resistoras shown in Figure 14. The coupler canhave a transistor, logic or SCR outputdepending on the type of circuit it interfaces.

ANY OUTPUT

GND

R1

Figure 14

Figure 15 shows how to drive a power FETsuch as an International Rectifier HEXFET.The driver circuits can both source and sinkhigh peak currents and were intended fordriving highly capacitive loads like this.

Applications GLOLABWireless Control

4

ANY OUTPUT

GND

Figure 15

You can interface to 5 volt TTL logic circuitsusing the voltage divider in figure 16.Optional diode D1 will improve turn off ofthe TTL circuit. R1=6.8K R2=4.7K

ANY OUTPUT

GND

R1

D1R2

TTLCIRCUIT

0V

+5V

Figure 16

Figure 17 shows a 12 volt relay that can beused to control any voltage including a 120volt AC circuit. This is a simple way tocontrol a lamp or floodlight. The relay maybe connected to any output. A 15 volt 500milliwatt or 1 watt zener diode D1 preventsdamage to the driver circuits from inductivespikes. Observe safety precautions whenworking with line voltage.

12 VOLTRELAY

ANYLOAD

15VZENER

ANY OUTPUT

GND

Figure 17

Solid state relays have built in currentlimiting resistors and can be driven directlyas shown in figure 18. These relays have atriac output for switching alternating currentloads.

ANY OUTPUT

GND

ACLOAD

SOLID STATERELAY

Figure 18

The circuit in figure 19 can be used toproduce a momentary output with a durationthat is controlled by the values of R2 and C1which form a time constant circuit.Maximum pulse width that can be achievedis limited by leakage current through C1. D2is a 4.7 volt zener diode that limits the resetvoltage to less than 5 volts. R1 can beconnected to either pin 3 or 4 of the latchingoutput. Reset must be connected to pin 8. Iflatch output pin 3 is used then programswitches SC1 and SC4 must be ON and ifpin 4 is used then SC2 and SC3 must beON. This circuit can be used when the twosecond momentary output is too short or toolong for your application. The value of R1should be a minimum of 1K and amaximum of 1MEG. The pulse width isapproximately R kohms X C microfarads / 4= TIME milliseconds. D1 is a 1N4001 thatdischarges C1 for fast recovery. 10 ohmresistor R1 limits discharge current.

LATCH OUTPUT

GND

RESET

C1

D1

D2

R1 R2

Figure 19