=====8 Channel Input Protector Kit===== NOTE: this page is not yet complete. The device will be available as soon as I have completed the build instructions. {{:kits:ip_hero.jpeg?600 |}} Arduino and other digital GPIO devices are becoming more and more important to our “smart homes” and security but are generally not designed with robust protection on their input lines. Your average Arduino CPU will have a protection diode on it’s inputs which is why you can more or less safely handle the bare boards but this will not protect it from larger issues associated with the long wire loops used for security or other sensor inputs. I have lost both arduino and other more expensive digital input devices due to induced current on long wires from lightning. You do not have to be hit by lightning or have any power surge on the power lines for this to happen. The long wires will act as an antenna and a potentially large current can be dumped through your device that way damaging the specific inputs or destroying the entire device. This board is designed to protect the digital input device from such events. The 8 Channel Input Protector works only with “contact closure” type inputs. It will not protect outputs, analog readings, or other communications. The device provides for optical isolation of the loops to the switches/sensors. This breaks the current path between your switch and your CPU input. No device can protect you from a direct lightning hit but this is not the most common mode of failure. If the surge event is too much for the protector to handle it may damage the opti-isolator on the protector board. This can act as a sacrificial component as it costs only a few dollars to replace at most and has none of the down time associated with ordering new devices, and if arduino then loading your own software and duplicating any other complicated wiring you may have setup to the device thus making your downtime much less likely and if it happens much less difficult and lengthy to set right. All the isolators on the board are socketed and can be replaced easily. All components are through hole, easy to assemble and robust. All connections are through removable headers. ----- ====Purchasing and Building==== This kit is not yet available for purchase. It will be available as a bare board, with a standard project case or with a 3D printed DIN rail mount. An already assembled and tested version will also be available. You will be able to purchase additional opti-isolators to have on hand just in case. [[protection:build|Kit Building instructions]] ----- ====Powering The Isolator==== {{ :kits:ip_power.jpeg?300|}} The board requires 2 power inputs, they can be the same if necessary though this reduces the isolation between the board and your device. There is an onboard power supply that powers the isolated side of the isolators and provides the voltage to sense the state of your contacts or switches. On the power connector this is labeled as “iso." This can accept from 3.3vdc to 24vdc. (note that the board says 5v to 24v but it will work just fine down to 3.3v) Below 5v the power led may be dim or change brightness as the indicator leds turn on and off, this is not a problem. The second power supply requires only a few milliamps and should be the power supply from your digital IO device or Arduino, or at least share the same ground as that supply. This second supply can be between 3.3vdc and 5vdc. Only CPU’s that operate between 3.3v and 5v are supported. This is the vast majority of Arduinos and other digital IO devices. All arduino devices have a way to get to the regulated board power and that is what you want to connect to this. The devices are usually only capable of supplying a few tens of milliamps which should be plenty to power this board. Both inputs are protected against reverse polarity but obviously wont work if you connect them that way. The Power LED will light indicating the isolated power is available and the onboard power regulator is operating. In order to verify that the CPU side power is available short one of the switch inputs to it’s common and the corresponding indicator LED will light up if all is working properly. ----- ====Connecting to the Arduino or Digital IO Device==== {{ :kits:ip_cpu_connection.jpeg?300|}} The input protector is compatible with devices that expect the input to be connected to gnd. This would be anything that is “input pullup” or that connects to gnd to turn the reading on and off. If the device needs to be connected to the positive voltage it will not work with this board. Connect the “To CPU” labeled terminals to the inputs on your device. ----- ====Using the Switch Loops==== {{ :kits:ip_contact_loops.jpeg?400|}} Eight switch loops are brought to removable headers at the bottom of the board. A port for the common is provided next to each actual input for easier wiring. If you already have all your commons brought together you can connect them all to a single common port on the board. There is no difference between them. The comm is at +3.3v. When connected to one of the numbered inputs it will turn on the opti-isolator which will connect the CPU connection for that pin to gnd. This is only suitable for simple contact closures, switches, leaf switches, relays and similar simple switches. This will not work with more complex devices with digital outputs, anything analog or anything that uses a serial type protocol to communicate. ----- ====LED Control Jumper==== {{ :kits:ip_led_jumper.jpeg?400|}} The status LED’s can be turned off by moving this jumper from the on to the off position. This can be useful if the device is in an area where the LED’s might be annoying after dark. It is also possible that some devices may have a very weak pull up and so may not accurately read the status changes while the LED’s are lit. They use very little current and I’ve tested with many different devices but this is still a possibility. If you are having trouble with it not sending changes to your device try turning the LED’s off once you don’t need the status displayed for basic wiring testing.