Differences

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--- fakerio_digital_input_tester [2018/12/18 22:45] – [Power LED] tell
+++ fakerio_digital_input_tester [2018/12/18 23:07] (current) – tell
@@ Line 47: / Line 47: @@
 Breaking down the schematic, here are the major portions.
-==== Input Connectors and LEDs ====
+==== DIO Connectors and LEDs ====
+{{ :fakerio-dio.png?200 |}}
+The schematic shows four copies, for four "channels."  Build as many or as few as you like.
+Each channel has the familiar 3-pin connecto, with power, ground, and signal.
+An LED lights up red when the signal pin is pulled low by a connected switch or sensor.
 ==== Power LED ====
@@ Line 59: / Line 65: @@
 If you've commonly got a 12v battery or power supply handy in your build space or lab, build this portion.  You might wire up the input to a set of red and black Anderson Powerpole connectors.
+{{ :fakerio-12vps.png?200 |}}
+The input is connected to the terminals at the left, drawn with "testpoint" symbols, which probably just map to single holes in the board for wires to be soldered in.
+Reading from left to right: The rectifier diode, D1, prevents any current from flowing at all if the power supply is hooked up backwards.  Next comes the PTC fuse, F1.  This is a [[https://en.wikipedia.org/wiki/Resettable_fuse|self-resetting fuse], sometimes called after the brand name [[ https://www.littelfuse.com/products/resettable-ptcs.aspx|Polyfuse or Polyswitch]]   If there's a short or too much current being drawn, F1 changes from low to high resistance essentialy opening the circuit.
+After the fault is removed, it automaticly resets.
+Here, we want to use a polyfuse that is rated to carry somewhere between 0.5 and 1 amp without opening the circuit.
+Next come some [[https://en.wikipedia.org/wiki/Capacitor|capacitors]], recommended to filter the power and keep the regulator chip U1 stable.
+U1 is the regulator integrated circuit, which makes stable 5v power from the input which can be anything from 8 to 13 or more volts.  The datasheet on the 7805 can be found here https://media.digikey.com/pdf/Data%20Sheets/ON%20Semiconductor%20PDFs/MC7800(A,AE),NCV7800.pdf
@@ Line 65: / Line 84: @@
 If you have a 5v power supply handy, for example a USB phone charger battery pack or wall brick, you might choose to build the 5v power portion.
+{{ :fakerio-5vps.png?200 |}}
+This power input circuit starts with a polyfuse, as above.  Then comes a diode for reverse-polarity protection, but its wired differently than in the 12v circuit above.  Here, the diode normally does not conduct, but if the input is reversed, the diode essentially shorts the power supply, protecting whatever is downstream.  This is likely to cause the polyfuse to open.