PIR sensor - Motion sensor

Yet another sensor! This time it's a PIR (Passive InfraRed) sensor: it reacts to infrared light emitted by warm objects or beings. It is called passive since it does not emit anything, just signals whenever it sense a variation of infrared light in its range.

Technical data (from the seller):

Range: 3m - 7m

Angle: 140° (approx.)

Trigger state duration: 3s - 200s

Power supply: 4.5V - 15V DC current

Output signal: 3V (alarm status), 0V (normal state)

Power consumption: <60uA (normal state)

Working temperature: [-15°C,+70°C]

Trigger mode: repeated sensing/non-repeated sensing

HC-SR04 : using multiple ultrasonic modules

In this note we are going to illustrate how three (or more) HC-SR04 modules can be used to add further "intelligent" vision to your bots. Basic usage of HC-SR04 and the principles on which it is based have already be given in this note.

The idea is to position the three sensors at fixed angles one another. Each module will give its own measure. Then, we use the three measures to try to induce some "safe/unsafe" state for our bot. In a safe state you can, for example, keep running forward. In an unsafe state, you can turn left or right according to the informations of the two other sensors. Indeed, consider the situation illustrated in Figure 1.

Figure 1. The general situation.

HC-SR04: ultrasonic sensor for Arduino

This week I will present one of the main ingredients of robotic constructions: ultrasonic sensors.

The physics

The sensor is based on a simple principle, sound echo phenomenon. A membrane emits an ultrasonic sound and a second membrane will catch the echo signal reflected by the obstacle.

Kick-off for the sensor library

This is my first attempt in writing a library for Arduino. The idea is to write some generic class for sensors. Specialized classes will implement each particular family of sensors. I would like also to start an independent sensor identification code. To uniquely identify each sensor component so that one can implement component comparisons and so on.

Here is an example of sensor (DHT11) which I would like to support. Here is the minimal code for the Sensor class.

Temperature & umidity sensor (DHT11)

According to LadyAda this is an extremely low-cost temperature and humidity sensor. Bah, for me 6 Euros are not nothing. Probably, other more sophisticated sensors are much more expensive… or they simply robbed me :-( 

From the data sheet I found that the pin out is as follows (from left to right w.r.t. the photo above):

1- Vcc (3.3V to 5.5V)

2- Data signal

3- Not connected (some people advice to connect it to GND)

4- GND

Sensor Shield (V6)

Just received this. To tell the truth I don't know why I bought it since I still have vague ideas and no huge project yet. Is one of that open eyes dreams or compulsive buying illness? However, I should try to use it now. OK, I'm planning to use for decoding the mini remote control signals (see this post).

The connectors of the IR receiver mini-board fits perfectly in the central rows of the shield (digital pin 3, +5V, GND). They seem to be conceived exactly for that. :-)

The mini IR remote control

In fact, this is not exactly the IR remote I have (see this post) but it has the same overall structure and number of buttons so I suspect that it comes from the same producer as mine and its codes are the same.

Indeed, this was the best photo I could find over the internet and that's the main reason for this picture here. Since I absolutely wanted to use the sensor shield (see this post), I mounted the sensor shield over the Arduino board and wired the IR receiver to the row containing digital pin 3 (right central part of the sensor shield). Following this excellent tutorial from Ladyada website I could decode all the signals sent by the remote control. You can find it on Github here. In a next post I will add some test program, in the meanwhile you can use the one provided by LadyAda tutorial.

Enjoy!

Lost treasures 1 (Cooling fan HY45J-05A-831)

Lost treasures

Disassembling old electronics pieces can be lot of fun. Sometimes one can find small treasures. I will start a series of posts with my findings. This time is the turn of a PC cooling fan. On the case I've found the model code: HY45J-05A-831. The manufacturer is SEPA. The are also minimal specs: 

DC 5V

0.16A

Here is a picture of the fan.