Raspberry Pi – Driving a Relay using GPIOThere’s something exciting about crossing the boundary between the abstract world of software and the physical . Although a simple project, I still learned some new things about the Raspberry Pi while doing it. There are only four components required, and the cost for these is around 7. Even a cheap relay like the Omron G5. LA- 1 5. DC can switch loads of 1. A at 2. 40. V. A word of caution: don’t tinker with mains voltages unless you’re really (really) sure about what you’re doing. A mechanical relay allows a safe learning environment, since you can switch any load with it (e.

A more efficient alternative to switch an AC load would be to use a solid- state relay (e. I recommend sticking with mechanical relays until you’re entirely sure about what you’re doing. Tip: you can buy plug- in low- voltage AC power- supplies if you want to play with triacs. The Circuit. There are four components to this circuit. A relay (5. V DC coil), a BC3. NPN transistor, a diode, and 1. K resistor. Essentially, the transistor is used to energise the relay’s coil with the required voltage and current.

A relay will often have 3 significant voltage/current ratings specified; coil, AC load, and DC load. The most important to our circuit is the coil rating, which is the current at a specified voltage required to energise the coil (activate the switch), sometimes expressed as milliwatts (m. W). The AC and DC load ratings relate to the switch- contacts, and state the maximum load current (e. DC loads are rated lower because they arc (spark) more, which eventually wears the contacts to the point of failure. In general, large loads need heavier contacts, which in turn need bigger coils to switch them, and bigger coils need more power from your circuit. Relays sometimes don’t fit easily onto a breadboard, so you might want to build the circuit on veroboard instead, or just mount the relay on veroboard and add two pins for the coil contacts (allowing you to breadboard it). Don’t ever put AC mains into your breadboard!

Schematic for a relay via GPIO on the Raspberry Pi. The GPIO pin used in the example code is GPIO. The choice of GPIO 1. I considered it less likely to conflict with other peripherals likely to be in use. Although the pin is marked 3. V on the schematic, don’t confuse this with the 3. V3 pin – I labelled it with the voltage to highlight that a 3.

1. Document Number: 83630 For technical questions, contact: optocoupleranswers@vishay.com www.vishay.com Rev. 1.6, 20-Oct-10 1 Optocoupler, Phototriac Output, High dV/dt.
2. A voltage-controlled oscillator (VCO) using the timer 555 is shown in figure. The circuit is sometimes called a voltage-to-frequency converter because the output.

Optocoupler Tutorial about how Optocouplers and Opto-isolators use light to electrical isolate its input signal from its output signal.

V GPIO pin is driving a 5. V load – it could also drive a 2. V coil, for example, if an appropriate DC power supply is used rather than the Raspi’s 5. V line. Essentially, to activate the relay, all the circuit does is send a few milliamps at 3. V from the GPIO pin, through a 1.

K resistor (you may choose to increase this to 1. K if you want to be strictly below 3m. A). This current is enough to saturate the BC3. V rail through the transistor, and therefore also through the relay’s coil. Most general purpose NPN transistors with an minimum h. FE of say 5. 0 to 1.

BC3. 37 – it will depend on a) how much current you’re willing to draw from the GPIO pin, b) how much current is required to energise the relay’s coil, c) the actual h. FE of the transistor in your hand, since they vary wildly and the current gain could easily be significantly more than the stated minimum. The diode in the circuit is there to conduct the current generated by the de- energising coil back across the coil (e. Similarly, take care to correctly identify the collector, base, and emitter pins on your transistor. The pin ordering varies by type, so check the datasheet.

I’d recommend you double check these two components before powering up. The breadboard photo shows it wired up. The pin numbering on my IDC plug should be though of from above the connector, to make it correspond with the 2. Blue is 5. V, and brown is Ground.

The green wire connects from GPIO 1. Raspi’s 2. 6- pin header) to the transistor base via resistor R1. You can test that the relay is working by disconnecting the wire from GPIO 1. V3 (pin 1). You should hear a click as you connect/disconnect 3. V3. Make sure you keep the resistor in the circuit (e. If it’s likely to also spend some time as an input, then a resistor (1. K would do) between the base and ground would ensure the transistor is fully off, rather than having a floating voltage applied.

Using the relay via the . It’s all in one file for simplicity and for clarity, though there’s not much to it. The usleep(1) call has been used to create a short delay before reading the LEVn register to feed back the pin status. This is because the rise time for a GPIO pin (the time for the voltage on the pin to rise to a level that’s considered . Unblock All Firewall Restrictions Surf Anonymously Browser.

Use at your own. * risk or not at all. As far as possible, I've omitted anything that doesn't relate to the Raspi registers. There are more. * conventional ways of doing this using kernel drivers. If the pin fails to go high, maybe you’ve got the original code.

Optocoupler Tutorial and Optocoupler Application. We know from our tutorials about Transformers that they can not only provide a step- down voltage, but they also provide “electrical isolation” between the higher voltage on the primary side and the lower voltage on the secondary side. In other words, transformers isolate the primary input voltage from the secondary output voltage using electromagnetic coupling by means of a magnetic flux circulating within the iron laminated core. But we can also provide electrical isolation between an input source and an output load using just light by using a very common and valuable electronic component called an Optocoupler.

The basic design of an optocoupler consists of an LED that produces infra- red light and a semiconductor photo- sensitive device that is used to detect the emitted infra- red beam. Both the LED and photo- sensitive device are enclosed in a light- tight body or package with metal legs for the electrical connections as shown.

An optocoupler or opto- isolator consists of a light emitter, the LED and a light sensitive receiver which can be a single photo- diode, photo- transistor, photo- resistor, photo- SCR, or a photo- TRIAC with the basic operation of an optocoupler being very simple to understand. Phototransistor Optocoupler. Assume a photo- transistor device as shown. Current from the source signal passes through the input LED which emits an infra- red light whose intensity is proportional to the electrical signal. This emitted light falls upon the base of the photo- transistor, causing it to switch- ON and conduct in a similar way to a normal bipolar transistor. The base connection of the photo- transistor can be left open (unconnected) for maximum sensitivity to the LEDs infrared light energy or connected to ground via a suitable external high value resistor to control the switching sensitivity making it more stable and resistant to false triggering by external electrical noise or voltage transients. When the current flowing through the LED is interrupted, the infrared emitted light is cut- off, causing the photo- transistor to cease conducting.

The photo- transistor can be used to switch current in the output circuit. The spectral response of the LED and the photo- sensitive device are closely matched being separated by a transparent medium such as glass, plastic or air. Since there is no direct electrical connection between the input and output of an optocoupler, electrical isolation up to 1.

V is achieved. Optocouplers are available in four general types, each one having an infra- red LED source but with different photo- sensitive devices. The four optocouplers are called the: Photo- transistor, Photo- darlington, Photo- SCR and Photo- triac as shown below. Optocoupler Types. The photo- transistor and photo- darlington devices are mainly for use in DC circuits while the photo- SCR and photo- triac allow AC powered circuits to be controlled. There are many other kinds of source- sensor combinations, such as LED- photodiode, LED- LASER, lamp- photoresistor pairs, reflective and slotted optocouplers.

Simple homemade optocouplers can be constructed by using individual components. An Led and a photo- transistor are inserted into a rigid plastic tube or encased in heat- shrinkable tubing as shown. The advantage of this home- made optocoupler is that tubing can be cut to any length you want and even bent around corners. Obviously, tubing with a reflective inner would be more efficient than dark black tubing. Home- made Optocoupler. Optocouplers and opto- isolators can be used on their own, or to switch a range of other larger electronic devices such as transistors and triacs providing the required electrical isolation between a lower voltage control signal and the higher voltage or current output signal.

Common applications for optocouplers include microprocessor input/output switching, DC and AC power control, PC communications, signal isolation and power supply regulation which suffer from current ground loops, etc. The electrical signal being transmitted can be either analogue (linear) or digital (pulses). In this application, the optocoupler is used to detect the operation of the switch or another type of digital input signal. This is useful if the switch or signal being detected is within an electrically noisy environment. The output can be used to operate an external circuit, light or as an input to a PC or microprocessor. An Optotransistor DC Switch. As well as detecting DC signals and data, Opto- triac isolators are also available which allow AC powered equipment and mains lamps to be controlled.

Opto- coupled triacs such as the MOC 3. A. For higher powered loads, the opto- triac may be used to provide the gate pulse to another larger triac via a current limiting resistor as shown. Triac Optocoupler Application.

This type of optocoupler configuration forms the basis of a very simple solid state relay application which can be used to control any AC mains powered load such as lamps and motors. Also unlike a thyristor (SCR), a triac is capable of conducting in both halves of the mains AC cycle with zero- crossing detection allowing the load to receive full power without the heavy inrush currents when switching inductive loads. Optocouplers and Opto- isolators are great electronic devices that allow devices such as power transistors and triacs to be controlled from a PC’s output port, digital switch or from a low voltage data signal such as that from a logic gate.

The main advantage of opto- couplers is their high electrical isolation between the input and output terminals allowing relatively small digital signals to control much large AC voltages, currents and power. An optocoupler can be used with both DC and AC signals with optocouplers utilizing a SCR (thyristor) or triac as the photo- detecting device are primarily designed for AC power- control applications. The main advantage of photo- SCRs and photo- triacs is the complete isolation from any noise or voltage spikes present on the AC power supply line as well as zero- crossing detection of the sinusoidal waveform which reduces switching and inrush currents protecting any power semiconductors used from thermal stress and shock.