Nuts and Volts - September 2017

connected to both RA0 and RA1 through signal diodes D1 and D2. When the Enter switch is activated, it pulls both RA0 and RA1 low at the same time. This allows two I/O pins to interface three input switches.

The signal diode D1 prevents the Left switch from also pulling RA1 low because it is reversed-biased. Likewise, D2 prevents the Right switch from pulling RA0 low. RA0 and RA1 are also configured to cause an interrupt whenever one or both of them go to a logic zero.

Critical to the operation of the Irrigation Watch is the sensing of water flow to the irrigation system, which is accomplished with a Hall effect water flow sensor shown

20 September 2017

REF QTY DIGI-KEY PT# MANUFACTURER PT# DESCRIPTION R1-4 4 1.2KWCT-ND FMP100JR-52-1K2 RES 1.2K OHM 1W 5% AXIAL R5 1 3.3KQBK-ND CFR-25JB-52-3K3 RES 3.3K OHM 1/4W 5% AXIAL Q1 1 2N3904FS-ND 2N3904BU TRANS NPN 40V 0.2A TO-92

D1-2 2 1N914B-ND 1N914B DIODE GEN-PURP 100V 200 MA DO35 C1-4 4 399-4151-ND C315C104M5U5TA CAP CER 0.1 μF 50V Z5U RADIAL RL1 1 HE113-ND HE721C0510 RELAY REED SPDT 250 MA 5V RV1 1 3362P-103LF-ND 3362P-1-103LF TRIMMER 10K OHM 0.5W PC PIN S1 1 458-1342-ND PK-11N40PQ AUDIO PIEZO INDICATOR 3-5V TH U1-4 4 160-1350-5-ND LTV-814H OPTO-ISOLATOR 5 KV TRANSISTOR 4-DIP U5 1 PIC16F1829-I/P-ND PIC16F1829-I/P IC MCU 8-BIT 14 KB FLASH 20-DIP DS1 1 67-1779-ND LCM-S01602DTR/A LCD MODULE 16x2 DISPLAY MISCELLANEOUS SW1-3 3 6 x 6 x 12 mm PCB mount momentary four-pin pushbutton tactile switch P1 1 .100 Pitch six-pin right angle header P2 1 .100 Pitch three-pin right angle header P3 1 2. 54 mm pitch 10-pin straight pin PCB screw terminal block connector Hall effect water flow sensor; working range 1-30 L/min, model YF-B5.

Enclosure, DIY 86 plastic project shell for DIY meter tester kit LCD1602 with buttons.

#4-40 hardware for mounting display and circuit board.

PARTS LIST

■ PHOTO 1. Close-up view of installed water flow sensor. This sensor has male hose connections, so I used two female hose to female pipe connectors on each end. Note the working range and model number.

■ PHOTO 2. Water flow sensor installed in water line that feeds my irrigation system. Note water cut-off valves on either side.

The 16x2 LCD display can be purchased on eBay from a China supplier for as little as $1.60 each including shipping. Shipping can take a few weeks. The display can also be found from US suppliers at a higher cost, but will ship much faster.

The pushbutton switches were purchased on eBay from “22newcentury.” Search "6x6x12 mm PCB Mount Momentary Four-Pin Pushbutton Tactile Switch w Green Cap."

The 2. 54 mm pitch 10-pin screw terminal connectors were purchased on eBay from “2015hiworld.” Search " 2. 54 mm Pitch

10 pin Straight Pin PCB Screw Terminal Block Connector."

The Hall Effect water flow sensor was purchased on eBay from “royalwaytrade.” Search "G3/4 Threaded Water Hall Flow Sensor Switch Flow Meter Water Control Copper," or just search "Hall Effect Water Flow Sensor." I think this is an industrial part used in vending machines.