Thursday, 12 May 2011

Invisible instrument - different modes

click to view larger image with readable text!

With the introduction of a 16x2 character based LCD display, and a dial (ok, in this instance a slider, but it should be a rotary dial) and some buttons, we can set the device into a number of different modes.

when tuning the input channels, the LEDs light up to show when a channel has detected a shadow and raised a "hit" value. In this case, because the LDRs were not inside their black tubes and the light is coming from behind, the camera actually cast a shadow onto the device, triggering two inputs!

Here we've set the device into "tuning" mode. It basically reads the input value from each channel/LDR and displays a message telling the user which way to "tune" the device. In an ideal world, each input should be around the half-way mark (reading a single-byte value of 128) so that changes in ambient light can be easily detected.
In this example, the display is showing that the "at rest" value is greater than 128 and so the user should adjust the pot on the first LDR. When the ideal value is reached (120-140) the LCD display will read "OK" and the user can use the slider to choose another channel to "tune".

It is important to use linear (not log) potentiometers for the tuners.
In fact, I didn't have linear pots to spare, and used log pots, but tuning is difficult because there is very little movement between too high and too low. A linear pot would be preferable here!