Electronic rain gauge

Tipping bucket rain gauge.

I built this rain gauge from common materials.

• Length of 90mm PVC storm water pipe.
• 90mm to 100mm PVC storm water converter
• Galvanised sheet (116 x 222mm) to make funnel.
• Plastic teaspoon (5ml).
• Small magnet.
• Reed switch.
• Insulating bushes.
• Stiff wire or paper clip (spindle).
• Solder lugs.
• Aluminium bracket.
• Steel attraction plate.
• Brass nuts and bolts.
• Araldite epoxy resin.
• Silicone sealant.
• Wire and solder.
• Terminal block.

• TLC555 or 7555 timer.
• 2 x 0.001 uF capacitors.
• 0.01 uF 16v capacitor.
• 1 uF 16v capacitor.
• 4.7K resistor.
• 10K resistor.
• 1M resistor.
• 1N914 diode.

The rain gauge has a metal funnel at the top which feeds water into the measurement mechanism. The mechanism comprises a plastic measuring spoon pivoted on a spindle and counter balanced with a small magnet. As the spoon fills with water, its mass eventually overcomes the counter balance mass and the attraction of the magnet to the attraction plate. The spoon then tips forward to release the water in the spoon. This action closes the contacts of an adjacent reed switch as the magnet swings past. The magnets weight then returns the spoon to its normal resting position as set by the brass screw. The brass screw is used to calibrate the amount of water required to tip the spoon by adjusting the distance between the magnet and attraction plate.
In order for spoon to tip it needs:
Funnel radius 11.1/2 = 5.55cm
5.55 x 5.55 x 3.142 x 0.02 = 1.94ml of rain to indicate 0.2mm.
To improve the resolution would require a larger funnel.

Note.

Reference.

Alternatives.