Make an Attiny13 based IR proximity sensor




This is an extremely cheap IR proximity sensor you can make with a few cheap parts and an AVR programmer. I use an Arduino as my programmer in this Instructable.

This sensor only has a range of about 3 inches. You can easily add more LEDs or brighter ones to extend the range. You can also easily re-arrange the LEDS to detect when a beam is broken as well.

The design takes advantage of a cheap AVR (computer on a chip). The computer pulses the IR LEDs off and on and compares the analog readings from the sensor in each state. When the reading with the lights on is above the reading with the lights off the sense pin goes high indicating the sensor is seeing it’s own (reflected) light. There is an LED on the sense indicator in this design so you can see when the sensor engages. You can connect the signal right to a microcontroller like an Arduino or Picaxe.
This design moves some processing out of your main robot brain and into it’s own node. You may want to debounce the signal, but you don’t have to flash the leds and take the readings. You can also use just one digital pin to take the reading. The sketch is around 700K out of 1024 available.

Make an Attiny13 based IR proximity sensor




Why I built this
I’m way out of high school, but this is part of a series of designs related to bringing the robots from the game Robot Oddysey into the real world. I want to allow grade schoolers the same chance to learn robotics I had. So I am working on building really inexpensive robots that can move in 8 directions without turning. The “bumpers” are complete now.

Step 1: Gather Materials

The electronics you will need are as follows. Digikey part numers and prices are as of 4/18/2012.

Quantity
Digikey Part Number
Description
Cost
1
475-1439-ND475-1439-ND
PHOTOTRANSISTOR NPN W/FILTER 5MM
$0.53
1
ATTINY13A-PU-ND
IC MCU AVR 1K FLASH 20MHZ 8PDIP
$0.95
3
CF14JT220RCT-ND
RES 220 OHM 1/4W 5% CARBON FILM
$0.24
1
CF14JT1M00CT-ND
RES 1M OHM 1/4W 5% CARBON FILM
$0.08
1
2N3904FS-ND
IC TRANS NPN SS GP 200MA TO-92
$0.18
2
754-1241-ND
EMITTER IR 3MM 940NM WATER CLEAR
$0.44
TOTAL
$2.42

You will also need

  • Electrical tape
  • plastic drinking straw
  • scissors
  • Wire snippers
  • breadboard and/or soldering iron
  • Jumper wires
  • An AVR programmer (any Ardunio compatible will do)
  • Ardunio 1.0 software with modifications to program Attiny and the Atiny13 core 

Step 2: Create a sensor shroud

You don’t want IR light leaking in from the sides of the sensor. We will create a little tunnel from electrical tape and a straw. My tape is opaque to IR. Yours probably is too but you can line it with aluminun foil if you want to be sure. Make sure no metal is exposed because it will ruin the circuit.

Cut off about 1.5″ (4cm) of the straw. Wrap it in electrical tape. Trim the ends and make it neat.

Cut about 1/2″ (8mm) bit of tape and roll it up from the short edge. Fold the roll in half. It won’t stay but put a good crease in it. This will plug the bottom of the sensor and keep stray light out that way.

Step 3: Prepare the sensor

Cut the middle leg off your phototransistor if it has one. It’s not needed in this design and can actually cause problems if you leave it on. You don’t have to cut it all the way back, but don’t leave very much.

Gently wiggle the sensor into the straw until the base is 1/4″ (5mm) in or so. Push in the folded roll of tape behind it and seal the back with a bit of tape.

Step 4: Wire it up

Make an Attiny13 based IR proximity sensor schematic
You can do this on the breadboard or solder it all together “dead bug” style. Do the breadboard first so you can program the Attiny13 easily. Once it works you can solder it together.

Follow the wiring diagram and keep some notes in mind.

  • The chip, LEDs and transistors only work one way around.
  • The short leg of the LEDS is connected to the 220 ohm resistors.
  • The long leg of the phototransistor is connected to the 1meg resistor.
  • You can add more IR emitter/resistor pairs in parallel with the existing pair. Get the basic circuit working first. You could also just use one IR emitter, but 2 seemed to make the readings a lot more stable.

Note: After I did this diagram I discovered a 0.1uf capacitor across the Attiny chip from VCC to GND helps out with stability. It’s recommended to put one across every microchip in a design. It worked reasonably in the breadboard without it, but the circuit board really improved with the addition.




This Post / Project can also be found using search terms:

  • attiny13a based led projects
  • & rgb led attiny13a
  • attiny based proximity sensor
  • attiny rgb led
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