Build Guide – dropControllerBT on a breadboard

The bread board version has LEDs to show when the camera and the solenoids are active and switches for draining the valves.

dropControllerBT Bread Board


Arduino Pins

dropControllerBT  Arduino Pins


Parts List: Bread Board Version

Bread Board x 2
Various wires
Arduino Nano x 1 (or any type of AVR based Arduino)
HC-06 Blue Tooth module x1 (HC-05 can also be used)
DC-DC step down power supply x 1 (can also use a LM7806 based circuit)
LEDs x 8 (9 if you want to add one to the power in)
– 3 x LED for camera trigger activity
– 3 x LED for solenoid valve activity
– 1 x Green LED for status – waiting
– 1 x Yellow LED for status – active
On/off switches x 4
– 1 x main power on/off switch
– 3 x solenoid valve drain
3.5 stereo sockets x 2
RCA/Phono sockets x 3
Power socket x 1
4N25 optocoupler x 3 (Anything similar also suitable)
TIP120 x 3
F9Z24N mosfet x 1 (or similar)
330 ohm resistor x 5
1K ohm resistor x 4
2K ohm resistor x 1
2.2K ohm resistor x 3
10k ohm resistor x 1
1N4007 diode x 8

3.5mm jacks to connect to the camera and shutter leads
RCA/Phono jacks to connect to the solenoid valves.

Of course, you will also need solenoid valves, a power supply and an Android device.

Circuit Diagrams

dropControllerBT Bread Board Circuit Diagram

Camera and flash triggers

The camera trigger circuit uses 4N25 opto-couplers as digital switches. Opto-couplers allow the Arduino to trigger the camera and flashes without having a direct electrical connection. The camera focus and camera shutter triggers use separate opto-couplers which then go to the same 3.5 connector. I have a Canon camera which requires both focus and shutter to be active for bulb mode to work.

Close up showing the opto-couplers
dropControllerBT Bread Board Optocouplers

Solenoid valve connections

The solenoid valves are controlled through TIP120’s. These are used as digital switches similar to the opto-couplers. The difference is the TIP120’s allow a larger voltage/current to be switched.

Close up showing the solenoid valve connectors.

Status LEDs

I previously used an LCD to show the device status and I suddenly realised I didn’t need this. I could show the same information using a couple of LEDs. A green LED shows when the dropControllerBT is waiting. A yellow LED shows when the device is active.


HC-06 Bluetooth Module

The HC-06 bluetooth module has power regulators to allow an input voltage from 3.6v to 6v. The module is actually a 3.3v device and only the voltage in pin can use a voltage larger than 3.3v. The RX and TX (receive and transmit) pins are still 3.3v. The Arduino will see a 3.3v as HIGH and so the TX pin of the BT module can connect directly to the RX pin on the Arduino (pin D2). This is not the same for the RX pin on the BT module. The RX pin is 3.3v in and we need to reduce the Arduino’s 5V to 3.3v by using a voltage divider. A simply voltage divider is 2 resistors in series. To convert 5V to 3.3v I use 1 x 1K and 1 x 2K resistor.

Note: A HC-05 in slave mode can be used instead of the HC-06.

As a quick guide to the voltage divider; 1K + 2K = 3K. 1K is a third of 3K so it reduces the voltage by a third.
One third of 5V is 1.66 and 5-1.66 = 3.33 which is what we want. Putting the resistors the other way would reduce the voltage by 2 thirds. For more information on voltage dividers have a look at the Sparkfun tutorial

Double check the resistors you are using. It is very easy to use the wrong values.

dropControllerBT Bread Board BT


The dropControllerBT device and the solenoid valves are powered from a single 12V wall wart power supply. The 12V power in goes to the solenoid valve connectors (through a diode) and also to a DC-DC step down converter. The converter reduces the voltage in to 5.7V. This goes to a 1N4007 which reduces the voltage to 5.0V and then connects to the Arduino 5V pin and the bluetooth module.
I am currently using a converter with a display to drop the 12V to 6V. When I eventually get round to putting this project in a case I will use a smaller converter with no display.
dropControllerBT Bread Board Power

Reverse Polarity

In an earlier version of the dropCopntroller, I had a weird problem, when the Arduino was connected to a computer by usb and at the same time the device was powered by the external power supply, the computer would crash when the usb cable was unplugged. I fixed this by adding a diode to the 5V out line on the Arduino. This stopped the computer crashing but unfortunately the diode ate too much power (fairly high forward voltage drop). I later swapped out the diode for a mosfet. The mosfet offers the same polarity protection as the diode but without the large forward voltage drop.

When there is power on the 5V line the mosfet is turned on and allows current to flow. Remove the 5V and the mosfet turns off.
dropControllerBT Bread Board Power