Project: Convert an inexpensive kitchen timer to a camera "intervalometer"

Introduction

The Radio Shack LCD timer is an inexpensive item that might be suitable for hacking, to convert it into a camera intervalometer.

Taking apart the hardware

Remove the 6 screws from the back plate:

(OPTIONAL) Remove the 4 screws holding the circuit board to the front button assembly.

Connect 2 wire-wrap style wires (solder in place) to the pads shown. These are the pads that connect to the 'start' button on the keypad.

(more images, including full-size high-resolution images, at my flickr page )

Proposed logic state diagram for intervalometer conversion project

Time Diagram

Buzzer_allow   -----|___________|--------------------

Buzzer         __|--|_______________________________

2pulse_wire    _____|---|___|---|____________________

Expose_button  _____|-----------|____________________

labels:          A  B   C   D   E

Description

• A) Buzzer fires when the user-set timer interval expires

• B) Expose button (relay) is triggered
  • Camera begins to takes a picture.
  • First pulse on output '2pulse_wire' is sent
  • Buzzer_allow (an inhibit style line) is set low. This prevents the circuit from being interrupted if the timer were to fire again, too soon. This also immediately quiets down the Buzzer, as it effectively acts as a SPST switch in series with the Buzzer.

• C) 2pulse_wire goes low. This is a virtual button-release event on the keypad of the timer.

• D) 2pulse_wire goes high. This is a virtual button-press event on the keypad of the timer. This is the 2nd press of the 'start' button on the timer - this has the effect of restarting the count-down, thus retriggering the timer for another cycle. At this point, the LCD display is now actively counting down, again.

• E) 2pulse_wire goes low.
  • This is a virtual button-release event on the keypad of the timer and is the final event of the 2pulse_wire line, for this cycle.
  • Expose_button is released.
  • Buzzer_allow is sent high, which closes the conceptual SPST switch in series with the Buzzer, thus allowing the user to hear the Buzzer when it fires next time, and also allowing our circuit to notice this event and act on it.