Electronic Circuits

The LED Metronome is a modern interpretation of a classic device which is a staple of music teachers, students and composers everywhere. This circuit uses 12 LEDs to simulate the sweeping motion of the pendulum and a speaker with a simple amplifier to generate a tick as the LEDs at the end of the arc are struck. It is adjustable from about 40 BPM to just over 200 BPM. When made in a Lexan or Plexiglass case it can add a fun ultra-modern touch to music practice (though most music teachers agree that you should never rely on a metronome to keep your beat).

1. The circuit will reliably run from 6 to 12V. A typical 9V battery will be drained in several days by the LEDs with constant use. A 6V pack made from AA, C or D cells will last much longer.
2. The circuit will need some calibration before use. Calibration is fairly easy and accomplished by using a stopwatch to count the number of beats. You'll want to calibrate for 60 BPM (one per second), 120 BPM (two per second) and 180 BPM (3 per second). Just use your stopwatch to find the points of R2 that correspond to those beat rates and the mark the dial appropriately. Next find 90, 150 and 210 BPM. By that time you should then be able to evenly mark the remaining positions on the scale.
3. Blue LEDs need about 5V to light, so if you intend to use blue you will need to remove R5.
4. For an ideal metronome effect, the LEDs should be arranged in an arc.

This IR remote extender can increase the range of most simple IR remotes (those operating on a 40KHz modulation) a significant distance. In use, the remote is pointed toward the detector on the circuit, and a button is pressed. The Sharp IR detector then decodes the 40KHz modulated signal into a series of pulses, which trigger a 555 timer. The 555 outputs pulses which are re-modulated and used to drive an IR LED. The circuit is excellent for use in a large room like a presentation hall where a typical IR remote is a bit weak. By extending the wires to the output LED (using shielded cable) you can control a device where line of sight isn't available (such as a wall full of TVs in another room).

Schematic

Notes

1. Only the CMOS TLC555 timer can be used in this circuit. The original NE555 cannot operate reliably at 40KHz. Acceptable substitutions are shown in the parts list.
2. Almost all powerful IR LEDs can be used for D1 if the appropriate value of R5 is chosen.
3. To calibrate the circuit, use a frequency counter. Connect it in parallel with D1 and then ground the base of Q1. Adjust R3 for 40KHz on the counter. If a counter is not available, you will just have to point a remote at the circuit, press a button, and then adjust R3 until it works. This can take a few tries as not all remotes transmit continuously.
4. If you intend to remotely mount D1 any great distance, you will need to use shielded cable. Connect the shield to circuit ground.

Parts

Schematic

Notes

1. Pushing and holding S1 causes the LEDs to rapidly cycle. Releasing the button locks the pattern and shows a number from 1 to 6.
2. When building the circuit, make sure to position the LEDs as shown on the schematic. Otherwise the pattern of the dice will look weird.
3. Two circuits can of course be both powered by one switch to make a dual dice.

Parts

hello sad