A people counter is a device used to measure the number and direction of people traversing a certain passage or entrance per unit time. The resolution of the measurement is entirely dependent on the sophistication of the technology employed. The device is often used at the entrance of a building so that the total number of visitors can be recorded. Many different technologies are used in people counter devices, such as infrared beams, computer vision, thermal imaging and pressure-sensitive mats

Infrared beams
The simplest form of counter is a single, horizontal infrared beam across an entrance which is typically linked to a small LCD display unit at the side of the doorway or can also be linked to a PC or send data via wireless links and GPRS. Such a beam counts a ‘tick’ when the beam is broken, therefore it is normal to divide the ‘ticks’ by two to get visitor numbers. Dual beam units are also available from some suppliers and can provide low cost directional flow ‘in’ and ‘out’ data. Accuracy depends highly on the width of the entrance monitored and the volume of traffic.
Horizontal Beam Counters usually require a receiver or a reflector mounted opposite the unit with a typical range up to 6 metres (20 ft), although range finding beam counters which do not require a reflector or receiver usually have a shorter range of around 2.5 metres (8 ft 2 in).
Vertical beams are somewhat more accurate than horizontal, with accuracies of over 90% possible if the beams are very carefully placed. Typically they do not give ‘in and out’ information, although some directional beams do exist.

Computer vision
Computer vision systems typically use either a closed-circuit television camera or IP camera to feed a signal into a computer or embedded device. Some computer vision systems have been embedded directly into standard IP network cameras. This allows for distributed, cost efficient and highly scalable systems where all image processing is done on the camera using the standard built in CPU. This also dramatically reduces band width requirements as only the counting data has to be sent over the Ethernet.
Accuracy varies between systems and installations as background information needs to be digitally removed from the scene in order to recognize, track and count people. This means that CCTV based counters can be vulnerable to light level changes and shadows, which can lead to inaccurate counting. Lately, robust and adaptive algorithms has been developed that can compensate for this behavior and excellent counting accuracy can today be obtained for both outdoor and indoor counting using computer vision

Main concept behind this project is to measure and display the number of persons entering in any room like seminar hall, conference room. LCD or seven segment display display placed outside the room displays this value. And when number of persons inside the room are zero, power supply inside the room can be cut using a relay interface. Second part of project serves the functionality of a door-latch opening using a password entered through keypad. As well as sending this data to a computer through serial port. This module also turn on buzzer if 3 wrong passwords are entered consequently. User can change this password anytime he/she wish using a keypad.

Rik Kretzinger grew up on a Christmas tree farm and spent his college years studying horticulture, but he found it too difficult to make a living as a small farmer so he spent most of his career working for others. 
A few years ago, he began to tinker with aquaponics (fishfarming + hydroponics), sensors and the open-source microcontroller Arduino to create an automated garden that could compete with commercial farms.

For the first couple of years he spent thousands of hours struggling to learn programming languages to automate his backyard mini-farm. Then while speaking at an international conference (along with Eric Maundu and Rob Torcellini, he’s among the elite few experimenting with aquaponics and automation) he was introduced to APDuino(open-source firmware for aqua- and hydro-ponics).

APDuino allows Kretzinger to read the sensors in his garden without any programming. Now Kretzinger’s garden can send him tweets or Facebook updates if something is going wrong and Kretzinger can adjust the water flow, pH and temperature from a smartphone.
Now, what started as a hobby may provide Kretzinger with the boost to compete as a small farmer. His plan is to keep it urban (or suburban). He’ll use unused backyards or vacant lots to grow his produce and he’s created a prototype tower (PVC structures similar to those in our videos of Rob Torcellini’s greenhouse and of rooftop hydroponics on Manhattan restaurant Bell, Book & Candle). 

His towers can be removed and taken to farmer’s markets where customers can “pick” their strawberries or lettuce directly from the units. His set-up is also highly mobile so if a property owner decides he wants his land back, Kretzinger can move within a week.

Rik Kretzinger’s blog: https://rik94566.wordpress.com/category/agponics-com/
Original story: https://faircompanies.com/videos/view/internet-farming-arduino-based-backyard-aquaponics/