Tag Archives: Arduino

Sensors for counting objects

In order to count anything, we need to detect it first. This usually means some kind of sensor. The sensor used will typically provide a signal that our counter can read. Most such sensors actually function as a type of switch because their output terminals are closing a circuit on the counter electronics that causes a count to increment.

The simplest sensor used to count objects is an actual physical switch. Microswitches are switches with very sensitive contacts: a light touch is all it takes to register the presence of an object. Often microswitches are made with levers to reduce the force needed or to have a greater reach.



One common application for this type of switch is in coin counters for arcade games. The coin falls through a slot,  tripping the lever as it rolls past the switch. The main advantage of microswitches is their low cost and reliability. A disadvantage of this type of counting sensor is that physical contact with the switch is required and the force required to trip the sensor can affect the object you’re counting.

Another common sensor type used as input to counters or object detectors is a photoelectric switch. This optical sensor detects the interruption of a beam of light, often invisible infrared light. For example, to count boxes on a conveyor belt, an emitter, typically an infrared LED shines a focused beam of light across the belt. When the beam is reflected by an object passing by on the belt, the detector sees the returned light and closes a circuit and this sends a pulse to the counter module, updating the count of items going by.


Optical sensors have the advantage of not requiring contact with the switch, but may not work well in dirty or dusty environments where the optical signal may be blocked. Also, this type of sensor used for counting reflective items can be “fooled” by multiple reflections, causing an inaccurate count. In this case, a through-beam sensor, where the item must pass between the LED emitter and its detector, is often more reliable.

Magnetic sensors, as their name claims, detect magnetic fields. They are very useful when a non-contact sensor is needed in a dirty environment where light may be blocked.


Now that we’ve got sensors to detect the items, our PRT232 counter module is the ideal interface to do the actual counting. We can make modifications to the basic counter, such as a display, or special RS232 signal outputs,

Arduino Programming: Turn water on with Arduino and solenoid valve

Arduinos are popular small microcontroller boards that have many applications. However, they’re not designed to switch loads above a few milliamps: say a couple LEDs or so. While power-driver shields do provide this capability, they also can consume more resources than you may be able to give up.

We developed a high current driver to make it easy to control a solenoid valves with Arduino. It will also control pumps and motors. With an adapter cable, it can easily connect to your Arduino, BeagleBone, Raspberry Pi or other digital controller without soldering or crimping any connections. Doesn’t get any easier than that.


The power driver board was born out of a need for controlling a 1 amp solenoid valve using an Arduino.  The solenoid valve was being used to control the water flow to fill a tank automatically. Now there’s a simple way to use your Arduino or compatible to switch up to 3A at 24VDC. Two output connections (the white wires shown above) connect directly the load (your solenoid, relay, motor, etc) and the power (red, black) go to the power supply (5 -24 volts). The orange lead is used to switch on and off. This is a low-voltage (5V) control that can connect directly to a microcontroller, or development board. An onboard LED indicates when the load is switched on.

Here’s some sample code that implements a timer with an Arduino. When the pushbutton is pressed, it turns on water flow for 3 seconds

// This sketch demonstrates a simple timer
// A load (motor, solenoid, relay, solenoid valve is on Pin 1
// A pushbutton to trigger the timer start is on pin 2
// When the pushbutton is held down for more than 0.1 second 
// then released, the timer starts
// and times out after 3 seconds
// Timer is retriggerable: if pushbutton pressed 
// during the timeout period, timer restarts
// Constant definitions
#define LOOP_INTERVAL 10
#define TRIGGER_PIN 0
#define OUTPUT_PIN 1

void setup()

void loop()
  static int count = 0;
  static int timer = TIMER_INACTIVE;
  // Process loop periodically
  // Check trigger input
  if (digitalRead(TRIGGER_PIN) == LOW)
    // Must hold down pushbutton for the entire interval and 
    // then release to trigger
    // push button released. Check if we should start timing
    if (count >= TRIGGER_INTERVALS)
      // Turn output ON (timeout is retriggerable)
      digitalWrite(OUTPUT_PIN, HIGH);
      timer = TIMEOUT;
    count = 0;
  // If timer active, count down
  if (timer != TIMER_INACTIVE)
    timer -= LOOP_INTERVAL;
    if (timer == 0)
      // Turn output OFF
      digitalWrite(OUTPUT_PIN, LOW);
      timer = TIMER_INACTIVE;

Let’s find out what new applications you can come up with.

Power Driver ($11.95 shipping included)