HVW Technologies Infra-Red Object Detection System (IRODS™)
Contents
1. 2000 HVW Technologies Inc IRODS User Manual v1 32. The following 4 steps illustrate a detection cycle 1 The V line is normally held HIGH 3V To begin a measurement sequence pull this line LOW OV Wait 56 ms 3 Scan the Vouw line s status If it is LOW an object was detected within the threshold distance If it is still HIGH 5V no object was detected 4 Raise the Vin line back to 3V for a minimum of 1 ms 3 ms recommended before beginning the next measurement sequence This resets the Vou register within the GP2D05 Since the result remains until explicitly cleared the host microcontroller need not have interrupt capability since the result will wait until the micro has time to read it 1998 2000 HVW Technologies Inc IRODS User Manual v1 3 IMPORTANT NOTE The output of the GP2D05 will float when not asserted It is good practice to use a weak pull up resistor LOK Ohm to 5V on the output blue wire If you experience erratic readings it is most likely that the floating output is causing the micro to see objects that don t exist Example Measurement and Calibration Routine for TIRODS using a BASIC Stamp II PO is connected to the voltage divider which in turn goes to Vin green wire P1 is connected to Vou blue wire START High 0 Make sure that Vin sees a high low transition Pause 3 Wait for it to be seen Low 0 Begin measurement sequence Pause 56 Wait for measurement sequence to complete If IN1 0 Then SHOW If object detect
3. The operating voltage of the unit is 4 4 7 VDC and should normally be run on 5 VDC 2 The input terminals maximum voltage rating is 3 V Exceeding this level may cause permanent damage ELECTRO OPTICAL CHARACTERISTICS Ta 25 C Vec 5V Parameter Symbol Conditions MIN TYP MAX Unit Distance Measuring Range AL 10 80 cm Output Terminal Voltage Vou Note 1 Vcc 0 3 V VoL Note 2 0 3 Average Supply Current Lec Note 3 10 22 mA Standby Supply Current Tecoff Note 4 3 8 uA Vin Terminal Current Te Vin 0V 160 270 uA Notes 1 Output HIGH 2 Output LOW 3 Average current during measurement period 56 ms MAX 4 Current consumption when Vin terminal is HIGH 1998 2000 HVW Technologies Inc IRODS User Manual v1 3 Mounting the Sensor The sensor unit may be mounted using the included piece of double sided foam or 2 appropriately sized screws Connecting to the Sensor A custom cable assembly is included with the IRODS kit The miniature connector is keyed so that it may only be inserted one way The following table shows the necessary connections Pin Symbol Wire Colour Connect To 1 Vin Green Voltage divider going to microcontroller pin MAX 3 0 Volts 2 GND Black Ground 3 Vout Blue Input pin of microcontroller 4 Vec Red 5 V DC The maximum voltage the input can tolerate is 3 V Use two 1K resistors included to make a
4. HVW Technologies Infra Red Object Detection System IRODS Overview IRODS is a low cost short range Infra Red IR alternative to ultrasonic detection systems By setting a detection distance threshold via a tiny potentiometer the user can reliably detect the presence of any object that comes within that distance Usable detection range is 10 cm to 80 cm approx 4 to 31 5 The IR Object Detection System consists of the Sharp GP2D05 Distance Measuring Sensor and a custom cable assembly The GP2D05 is a compact self contained IR object detection system incorporating an IR transmitter receiver optics filter detection and amplification circuitry The unit is highly resistant to ambient light and impervious to variations in the surface reflectivity of the detected object Unlike many IR systems IRODS has a fairly narrow field of view making it ideal for sensing even small objects such as candlesticks The field of view changes with the threshold distance see the graph at the end of this document but is no wider than 10 cm 5 cm either side of centre when set at maximum range Specifications ABSOLUTE MAXIMUM RATINGS Ta 25 C Vec 5V Parameter Symbol Rating Unit Supply Voltage Vec 0 3 to 10 V Input Terminal Voltage Vin 03 To 3 V Output Terminal Voltage Vo 0 3 to 10 V Operating Temperature Topr 10 to 60 C Storage Temperature Tytg 20 to 70 C NOTES 1
5. IR remote controls have shown that even with 2 or 3 remotes pointed at the GP2D05 the unit still functions normally Laser Light Tests with a laser pointer had results similar to the flashlight only a beam aimed straight into the sensor s receiver would cause a false reading If the beam comes from even a few degrees off center it has no effect How Does it Work Figure 2 shows how the GP2D05 uses an array of photodiodes called a Position Sensitive Detector or PSD and some simple optics to detect distance An infra red diode emits a modulated beam the beam hits an object and a portion of the 1998 2000 HVW Technologies Inc IRODS User Manual v1 3 light is reflected back through the receiver optics and strikes the PSD In figure 2 Object A is closer and therefore the reflected light from it enters the receiver s lens at a greater angle than does light from object B Here Object A is at the limit of the PSD s range about 10 cm away Notice how that if it were any closer the light would not hit the PSD at all Similarly if B were moved farther away its light would eventually go past the top of the PSD and would not be seen either at about 80 cm This explains why IRODS has these limits Fig 2 Think of the PSD as a resistor with a large number of taps wires coming out at various points along the resistor When light hits the PSD it hits one of the taps and causes current to flow out ea
6. ch end of the resistor forming a voltage divider similar to that of figure 1 As an object moves closer or farther from the sensor incoming light hits a different tap causing the current coming out each end of the resistor to change These currents are compared and a voltage proportional to the position of the tap and hence the distance of the object is generated This voltage is compared with the voltage that you set with the threshold pot to determine whether the V ou line should be sent low A block diagram of the inner workings of the GP2D05 can be found at the end of this document CAUTION The GP2D05 is a precision device DO NOT attempt to open the unit Doing so will ruin the delicate alignment of the optics Detection Distance vs Sensing Range HVW Technologies Inc 3907 3A St N E Unit 218 Calgary Alberta T2E 6S7 Sensing distance 80 cm CANADA Tel 1 403 730 8603 Fax 1 403 730 8903 http www hvwtech com support HVWTech com Detection distance L cm E Outline Dimensions Unit mm Emitting portion Detecting portion Light detector PSD Le ea IR LED evig VR Threshold set PSD Position Sensitive Detector JAPAN SOLDERLESS TERMINAL MSG CO The dimensions marked with 4 are described made connector S4B ZR as the dimensions of lens center position Reflective object 1998
7. ed tell me Goto START No object detected start over SHOW Debug Object Detected cr Display Object Detected in debug window Pause 5000 Wait 5 seconds remove when done calibrating Goto START Start over END Using Multiple Sensors In order to minimize the number of I O lines required we suggest that when using multiple sensors that the Vip lines be connected together and brought to a single output pin on the micro This means that all sensors will start measuring at the same time but you will only need 1 input per sensor plus output to start them all Using this techniques an effective obstacle avoidance system for a mobile robot such as our Mobile Robotics Platform MRP can be implemented using only 3 I O lines for 2 sensors Since the V line draws only microamps many sensors can be connected like this Some Observations on the Effect of Different Kinds of Light Ambient Light Tests have shown the GP2D05 to be highly immune to ambient light levels Incandescent fluorescent and natural light don t appear to bother it The only instance where we were able to get it to falsely trigger was when a flashlight was pointed directly into the sensor s receiver even a few degrees off centre is enough for the sensor to ignore it IR Light The GP2D05 uses a modulated IR beam to guard against false triggering from the IR component of incandescent fluorescent and natural light Tests with several kinds of
8. voltage divider fig 1 1K To Microcontroller Pin To Vin Green wire of GP2D05 Fig 1 Calibration To calibrate the unit to the desired threshold distance carefully turn the small potentiometer next to the connector with a jeweller s screwdriver CAUTION The potentiometer is delicate use a screwdriver with a very small blade and make adjustments with the least amount of pressure you can the sensor was not designed to be adjusted continuously so try to set the distance once and leave it To set the threshold distance closer turn the pot counter clockwise To set it farther turn it clockwise The amount that the potentiometer must be turned for a particular change in threshold setting is very small 1 64 of 1 turn will produce a noticeable change Note that turning the potentiometer during a measurement sequence will invalidate the result Therefore you must cause a single measurement sequence adjust the pot then initiate another sequence A program suitable for calibrating the unit is shown below Operation The GP2D05 makes repeated measurements before it indicates the presence or absence of an object The time it takes to make these measurements varies slightly from unit to unit and can be from 28 ms to a maximum of 56 ms We recommend that you allow the full 56 ms just to be safe If you have a time sensitive application you should experiment with the specific unit s you have to determine the minimum reliable measurement time
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