List of Miscellaneous

Here is the list of miscellaneous: 

• RLA .................................... 5v p.c.b mounting miniature relay 200mW nom operating power (2 pole changeover)
• S1 .......................................  3-pole 4-way rotary switch, break-before-make 
• SK1 ....................................  2.5mm power socket, single hole fixing with break contact
• SK2 ....................................  3.5mm open mono jack socket
• WD1 ..................................  low profile wire-ended piezo electric sounder 

List of Semiconductors

Both figure above showed the list of semiconductors: 

• D1 .......................... 5mm l.e.d 
• D2, D3 .................. 1N4001 50v 1A rect diode (2 off)
• TR1 ....................... 2N3904 npn low power transistor
• TR2 ....................... BC337 npn medium power transistor
• IC1, IC2 ................ ICM7556IPA low power dual timer (2 off)
• IC4 ........................ LM2940HCT 1A low dropout regulator
• IC3 ........................ HCF4520BEY dual binary counter 

List of Capacitors

This is the list of capacitors that needed for the Body Detector circuit: 

• C1, C4 .............100p metallised ceramic plate, zero temperature coefficient (2 off)
• C2, C5, C9, C13 ...... 100n metallised polyester film (4 off)
• C3, C6.............. 100micro sub-miniature radial electrolyte 10v (5 off)
• C8 .................... 4n7 multilayer metallised polyester film
• C10 .................  150p metallised ceramic plate, zero temperature coefficient 
• C14 .................  100n metallised polyester film 
• C15 .................  1000micro miniature radial electrolytic 10v
• C16 .................  10micro sub-miniature radial electrolytic 35v 
• Cx ...................  a variety of metallised ceramic plate from 1p to 100p. 

All metallised ceramic plate capacitors have zero temperature coefficient

List of Resistors and Potentiometers

Here is the list of the resistors that need and involved in the Body Detector circuit: 

• R1, R2, R4, R5, R7, R10 ................................................................  10k (6off)
• R3 ..................................................................................................   470kOhm
• R6 ..................................................................................................   3M3
• R8 ..................................................................................................   270k
• R9 ..................................................................................................   150k
• R11 ................................................................................................   100k
• R12 ................................................................................................   2k2
• R13 ................................................................................................   220k
• R14 ...............................................................................................   15k
• R15 ...............................................................................................   68ohm 

All metal film 0.6W 1% (50ppm/ ohm C temperature coefficient)


List of Potentiometers:

• VR1 ........................ 200ohm to 500ohm 10 or multi turn wirewound potentiometer 
• VR2, VR3 .............. 50k 18 or multi turn horizontal cermet preset (2 off) 
• VR4 .......................  470k vertical sub-miniature carbon preset, linear cermet preset 100ppm/ degree circus temperature coefficient

Body Detector Components

This is the list of the Body Detector component:

 

Calibration

To undertake initial setting-up, use a test lead terminated at each end with a crocodile clip. Attach one end to the sensor bolt and the other to a piece of tin-foil about 300mm square. Due to the sensitivity of the circuti, it is important that both ends of the test lead should have a sure connection. Turn carbon preset VR4 back completely. Turn multiturn preset VR3 to 40 kilohms (40k) and multiturn preset VR2 to its maximum setting 50k. Turn the multiturn potentiometer VR1 to its mid-point. If at any time the circuit does not behave as described, switch off immediately and check the wiring carefully. 

Be aware that the presence of your body may affect the turning. Use a plastic or insulated screwdriver to turn VR2 and stand back from the circuit to see weather the crackling stops. If not, continue to back-off VR2 very carefully until the crackle just stops when stand back. Now set switch S1 to activate. The unit should now react when your hand approaches the sensor plate from a distance of few centimeters. Experiment a little to discover the best setting for preset VR2 and potentiometer VR1. A single "crackle" triggers monostable IC2b. 

Note that that the Activate position of S1 is optimised both for small sensors such as the 300mm square tin-foil sensors used in testing and a moderate temperature range (10 degree circus or 15 degree circus variation). Other application may require calibration in the Activate setting, monitoring the voltage across capacitor C10 by means of the test bolts provided. 

Casing Up without Circuit

The Body Detector is built into a plastic case with slotted walls, size 158mm x 95mm x 54mm approx. Holes are prepared on top of the case for VR1, S1, L.E.D D1, and the sensor bolt. Two small holes are also carefully positioned on top of the case to expose multi-turn presets VR2 and VR3, so that these may easily be adjusted from outside the case.

 

It is suggested that the holes for the presets be clearly labelled, so that their purpose is not forgotten with the passing of time. The author has more than once returned to a past project, only to puzzle over what the various adjustments might once have been for. Power socket SK1 and jack socket SK2 are mounted on the back of the case. Drill a hole for the insertion of a thermometer. 

 

The test bolts and piezo disc WD1 are mounted on the case. The piezo disc may be mounted behind a small hole on the front wall of the case. Board B is slotted into the case with the multiturn cermet presets VR2 and VR3 face downwards. Cable ties may be used to tidy up the connecting wires. Make sure that the battery is secure since a change in its position inside the case could slightly affect the unit's calibration.

Switching ON

Since the Body Detector is intended to detect any and all body presence, an On/Off switch that is mounted close to the circuit could in some instances present a problem. At the same time, to include any delays in triggering might be self-defeating, since some applications will require instant triggering such as a "turnstile counter" or an anti-tamper alarm.

A key switch was thought to be the most obvious solution for switching off and may be located some distance from the circuit. This may be inserted in place of (in series with) S1a. Best of all, any delays in triggering should be included in the external circuit. The author mounted the on/off switch on the case for the purpose of neatness and easy setting up. In most applications, this did not cause the circuit to trigger when switching off. 

However, solder pins have provided for compensation capacitors (Cx) at poitions E8 and E9 on the oscillator board. Their insertion may be left until the circuit is complete and is found to be working satisfactorily. 

Preliminary Tests

Meaningful testing can only be carried out once the oscillator board has also been completed and connected up. For the time being, it may establish that regulator IC4 is supplying the correct voltage. Attach a 9v PP3 battery to the battery clip, switch S1 to any position other than Off and measure the voltage across capacitor C15. This should be close to 5v. The regulator i.c should remain fairly cool and supply current should not rise above 15mA.

If any specified components for the Body Detector cannot be sourced at this stage, it is important that equivalents should have low temperature coefficients particularly capacitors C1 and C4 which should if possible have a zero temperature coefficient. The multiturn  potentionmeter VR1 may be pricy. however, these devices may sometimes be obtained cheaply as surplus goods. Alternatively, use a cheap 470ohms or 1 kilohms potentiometer, although this will not offer the same high degree of precision when it comes to calibration. 

OSCILLATOR BOARD

Having completed the preliminary checks, we can now tackle the construction of board B, which includes the h.f.o.s, the l.f.o and monostable. We shall also be casing the unit and calibrating it. Taking the second piece of strip-board, again having 18 holes by 34 cooper strips, create the breaks in the underside copper tracks with with a drill bit or other appropriate tool. Details of the topside component layout together with the underside details. 

Solder in position the wire links and solder pins, then the dual-in-line sockets then the resistors and multiturn presets continuing with the capacitors. Be careful to observe the correct polarity of the electrolytic capacitors and the correct orientation of IC1 and IC2, when inserting them into their holders. Pin 1 of IC1 and IC2 lies close to the small indentation on one of their encapsulation. 

Next, prepare seven sheathed wires 15cm long and solder them to potentiometer VR1, the sensor solder tag and sections S1b and S1c of the mode switch. Finally attach the leads from VR1 to the solder pins on the topside of the strip-board, the wire from the sensor solder tag and then the eight colour-coded wires from board A. Jack socket SK2 is included for switching small external loads- a second jack socket may easily be added. solder pins have been provided for this purpose at the opposite side of relay RLA at board position R9 and R13 on board A. the specified relay is rated at 60W 250V a.c and would therefore also be capable of switching small a.c resistive loads.

Construction

The Body Detector is built up on two pieces of strip-board each having 18 holes by 34 cooper strips. We start construction with board A. This holds the regulated power supply, the digital mixers (IC3), the inverter and the relay.  Details of the topside component layout together with the underside details are shown in figure above. All components should fit into place without difficulty, provided that miniature radial capacitors are used. 

 

Commence construction by cutting a standard piece of strip-board down to size using a hacksaw. Create the breaks in the underside of the strip-board with a handheld drill bit or other appropriate tool. Solder in position the wire links and solder pins, then the dual-in-line socket, then the resistors, the relay and the diodes continuing with the capacitors, transistors and voltage regulator IC4. The polarity of the piezoelectric sounder WD1 is unimportant. 

Be careful to observe the correct polarity of the electrolytic capacitors and the correct orientation of the regulator, the transistor, diodes, L.E.D, relay and IC3. Pin 1 and IC3 lies close to a small indentation on one end of the encapsulation. The cathode (k) of L.E.D D1 has the shortest lead and the cathodes (k) of diodes D2 and D3 are banded.

Prepare seventeen sheathed wires 15cm long- eight of which are colour-coded. The colour-coded wires attach to the oscillator board (board B) later. Solder wires to Mode switch S1, power socket SK1 (power in), jack socket SK2 (out), L.E.D. D1 and two solder tags which each attach to a Test bolt as shown. Finally attach the leads from S1, SK1, SK2,D1 and the test bolts to the topside of the strip-board and connect the colour-coded wires to the solder pins as indicated in figure 7. 

Check that all the wire links and components are correctly in place. Check that the track breaks are all there and in the correct positions. and that there are no solder bridges on the board. The author routinely runs a thin, sharp screwdriver down between all the strip-board tracks.

Schematic Diagram of Body Detector

The full circuit diagram for the Body Detector is shown in figure above. IC3 is a CMOS 4520 dual binary counter, which is wired as a dual binary mixer. Many mixers in similar applications employ a charge pump to detect a difference frequency. However this tends to be an art as much as it it science. The 4520 dual binary counter enables precise digital detection, potentially to an accuracy of about 1Hz at frequency up to 5MHz.

Benchmark high frequency oscillator (h.f.o) IC2a clocks binary counter IC3a, while sensor-h.f.o. IC1a resets the counter at around the same frequency. These two inputs far from simply cancelling each other out, produce a waveform as in figure 6a, when a larger difference frequency is present and as in figure 6b when the difference frequency is close to the null point. It then remains merely to detect the troughs in the waveform when exceed a specific duration (e.g 50ms). This is accomplished through binary mixer IC3b.

The mixed signal (the difference frequency) from IC3a is fed to the reset pin 15 of binary mixer IC3b. The low frequency oscillator (i.f.o) IC1b feeds the clock input of binary mixer IC3b. The clock input is completely cancelled out by the reset pulses, unless the duration of the troughs at the reset pin falls below the frequency of the clock input. In this case, the clock pulses break through. With the component values shown, the frequency of the i.f.o is fixed at around 500Hz- that is 500Hz away from the null point. 

:: TIME DELAY

  

At this stage, the output of binary mixer IC3b at pin 12 is not particularly useful and first needs to be inverted before triggering monostable timer IC2b. This is accomplished with the help of transistor TR1. With the component values shown, monostable IC2b may be adjusted over a useful 150ms to more than 30seconds by means of preset VR4. If different timing periods are required, capacitor C12 may be altered accordingly. 

The output of monostable IC2b at pin 9 provides current for switching transistor TR2, which in turn controls relay RLA. A variety of miniature relays would be suitable here, provided that the norminal operating power does not exceed 500mW. Diode D2 suppresses back e-m-f when the circuit is broken.

A delay is provided at switch-on in the form of capacitor C11 and resistor R9. this arrangement produces a negative pulse for a few seconds at IC2b's reset pin, so that the user sufficient time to step out of range before the Body Detector is activated. The delay is reactivated in the Sleep position setting of rotary switch S1. 

Low dropout regulator IC4 is used to ensure a steady supply voltage. Any similar regulator may be used on condition that it is rated 150mA or higher. With the specified low dropout regulator, the unit's power consumption is typically 13mA or standby and up to 100mA when triggered. 

An alkaline PP3 battery should thus give two days continuous service. the battery option is provided mainly for freeing up the unit during testing, and for demonstration purpose. The option of an external d.c power  supply (7v to 26v) is included. The circuit is reverse-polarity protected through diode D3 although the regulator itself is virtually indestructible. 

Block Diagram

  Sensor H.F.O  IC 1a (ICM7556IPA)  

•  is an RC oscillator, so that when its metal sensor is approached, C increases and frequency drops, creating a frequency difference between the two H.F.O oscillators. 

•  reset the counter at around the same frequency.

 L.F.O IC1b (ICM7556IPA) 

• the low frequency oscillator.
• detect only the smallest different frequency. 
• feeds the clock input of binary mixer IC3b.  

 Benchmark H.F.O  IC2a (ICM7556IPA)   

• improve the circuit's stability, so that the unit has intelligent frequency compensation (as opposed to temperature compensation, which merely reacts to environmental conditions). 
• clock binary counter IC3a.    

 Two binary mixer, IC3a & IC3b (HCF4520BEY DUAL BINARY COUNTER) 

•  wired as a dual binary mixer in this circuit.
•   employ a charge pump to detect a difference frequency.
• will detect frequency variations to within a small fraction of one per cent. it has a high degree of accuracy as well as flexibility. 
• it could have a wide range of possible applications, such as a detection of body capacitance for this project.
•  these mix a signal from high frequency oscillator, IC2a with a benchmark frequency produced by IC2a

Inverter (TR1, 2N3904 npn low power transistor) 

•  the output of binary mixer IC3b at pin 12 is not particularly useful and first need to be inverted before triggering monostable timer IC2b. this is accomplished with the help of transistor TR1. 

Negative pulse at switch ON (C11 & R9) 

•  A delay is provided at switch ON in the form of capacitor C11 and resistor R9.
• This arrangement produces a negative pulse for a few seconds at IC2b's reset pin, so that the user has sufficient time to step out of range before the body detector is activated.  

Monostable and Relay, IC2b (ICM7556IPA low power dual timer)

•  the output of monostable IC2b at pin 9 provides current for switching transistor TR2, which in turn control to relay.
• monostable IC2b may be adjusted over a useful 150ms to more 30second by means of preset VR4. 

Circuit Application

Due to its high sensitivity and good stability, the Body Detector may be attached to a wide variety of metal objects in the process sensitizing the entire object concerned. Although in theory the Body Detector is dependent on the electric field which surrounds the human body, in effect it acts as though an invisible field were created around the object concerned similar to the "invisible" defence shields seen in the latest star wars movie.

From a practical point of view, the sensor may include any object from the size of a pin to about 70kg in weight (e.g lightweight motor-scooter). However the greater the weight of the metal sensor, the less the sensitivity of the circuit. the more critical the tuning and the more it becomes susceptible to temperature variations especially. 

If attached to lighter metal objects such a sheet of tin-foil, the Body Detector may be turned to detect a person's presence up to 80cm away. At several centimeters distance, the circuit is sufficiently stable to avoid spurious triggering over a wide temperature range. In one test,  bicycle was moved from shade to full sun and back into the shade during the course of a day, maintaining reliable triggering. In another test, a 300mm square of tin-foil was tested successfully without the need for readjustment between 10degree circus and 0 degree circus and would in fact have exceeded this. This compares very favorably with variations in room temperature which typically amount to no more than 10 degree circus.

Limitation of Body Detector

The limitation of Body Detector is : 

1) it can only detect a presence of human at up to 80cm away only.

2) the sensor may include any object from the size of a pin to about 70kg in weight only.

3) the greater the weight of the metal sensor, the less the sensitivity.

4) over a modest temperature range, e.g 10*C to 25*C. 

5) in a single application only. 

Scope of Body Detector

 

THINK..what is the possible applications that could be by using the Body Detector?  

  

• Pressure-less Pressure -Mat  - which would detect the presence of a person passing over it or past it. it could serve as an alarm or a "turnstile counter".  
•   
•  Invisible Switch - set for example into a concrete wall. Among other things, this could serve as an invisible "panic button". 
•  
• Safety Switch - which would render an entire area a safety zone. This could shut down dangerous machinery or child-proof certain areas.
•  
• Defence Shield - if a thin length of wire were used for the sensor and run down a passageway or across a room,a "defence shield" could be created to cover a considerable walking area.
•  
• Safe Area - a detector wire could be circled around a tent or sleeping-bag when camping to detect footprints (but unfortunately not spiders or hyenas). 
•  
• Touch Sensor - the Body Detector could be attached to metal items of value such as a computer system-unit or a bicycle, to trigger an alarm merely when the paintwork is touched.
•  
• Temper Alarm - it may be used to prevent tampering with, for instance burglar bars or a yale lock. 
•  
• Sensor - could also be placed behind items of value or in front of them such as paintings or antique items of furniture to protect them from theft or abuse.      

Body Detector

Create your own "invisible" protective shield and let the force be with you!

Capacitance is an extraordinary phenomenon in that it is able to work through empty space. This is a quality that is normally taken for granted. The accumulation of charge on a metal plate gives rise to an electric field, which will affect another plate in direct proportion on the inverse of is distance. Capacitance is also one of a vast range of physical phenomena that may be translated into electrical oscillations.

The Body Detector relies on the fact that human body itself possesses a fairly large order of capacitance to the ground (earth) and that if such a body approaches the positive plate of a given capacitor, its value will rise. If then, one could find a means to detect such an increase in capacitance, one would have an effective means of detecting the presence of human body.

In the presence application, a metal sensor is attached to the positive plate of timing capacitor of an RC oscillator, so that when a human body approaches, the value of C increases and the frequency of the RC oscillator decreases. This drop in frequency is detected digitally and is used to switch a relay.  

UV Board Making Step.... (STEP 1)

STEP 1: Preparing circuit

This is the packaging of UV board

PCB circuit layout on transparent paper

a) On a transparent film,start your layout with transfer paper 

b) Print your circuit on white paper then copy on an acetate film 

This is UV box

c) Direct copy the circuit on transparent film by using duplicator 

d) Print out from computer plotter  

e) Prevent the printed transparent film from expose to sunlight after duplicating

 

"Everything is hard before it become too easy"

UV Board Making Step.... (STEP 2)

STEP 2: Exposing 

Put the printed transparent PCB layout in center position on the board

a) Cut the board to a size you desired if necessary
b) Tear off the black protection film on the board

c) Expose the board in Exposure box for 60-90 seconds

d) Put your circuit layout on top then press a flat glass sheet as a top layer to make a good contact between the film and surface of board

e) Turn on the light for 8-10 minutes 

f) Good contact between the film and the board is very important

      "Suit the action to the word, suit the word to the action"

UV Board Making Step.... (STEP 3)

STEP 3: Etching 

Etching Tank

a) Etching the board in etching tank for 4-10 minutes

b) Pour enough etching solution (Ferric Chloride) into a plastic tray and immerse the board with artwork side up

After come out from the etching tank

c) Gently agitate the tray till the unwanted copper foil etched away and only the circuit pattern left

d) Rinse the board with plenty of water

e) 15-60 minutes maybe required to etch the board completely

f) The etching process is most effective if the solution is kept at a temperature of about 120-140F (50-60C) 

 

Here short video that taken when we doing the etching process

 

"Creativity is allowing yourself to make mistake. Art is knowing which one to keep"