A brief description:

Using 12V power input, it can work at 9~18V (limited by the NE555 limit operating voltage).

The original design was also covered with a patterned acrylic panel, but it was not designed and only a 3D printed lampshade was used to even out the light.

Principle analysis:

Let’s analyze the left side first. The left side is a voltage and current conversion circuit composed of a triode.

The output current is (base voltage - emitter junction voltage drop) / emitter resistance.

On the right is a PWM generator composed of NE555, with an adjustable duty cycle of 0.1%~99.9%.

Charging circuit: D7->VR2 upper half->C10

Discharge circuit: C10->VR2 lower half->D8

Ignoring the diode conduction voltage drop, the time of one cycle is 0.693xVR2xC10.

C1 and R1 form a differential circuit, which does not have high frequency requirements, so the calculation is not carried out.

R2 is used to discharge C1 in preparation for the next trigger.

Combined with the following parts, this is actually a monostable trigger circuit composed of 555.

The ones on the left are used to generate reference voltages. In a series circuit, the voltage ratio is equal to the resistance ratio. No need to explain much.

The two extremes of the potentiometer are 1:1:1 and 1:2:1.

The right side is used to charge and discharge the capacitor with constant current. The formula is the same as the LED driver above. This makes the triangle waveform straighter.

(The old version is an ordinary monostable, without constant current, and the effect is not that good, but it has many fewer components)

Auto-start after power-on means that all channels are set high at the same time, and then the monostable circuits are triggered one by one.

Real machine operation:

The following operations are to switch color speed, brightness, power on, power off,

Video address: https://www.bilibili.com/video/av75030337/

Production process:

The two 555s on the right burned out and became very hot when powered on, so I replaced them with my own. The rosin could not absorb the 1-pin copper-clad pads cleanly. (The PCB has now been changed to include smaller copper-filled heat dissipation connections)

Hardware BUG:

Design problem, it is slightly bright when OFF. The NE555 (U4) on the right will be improved by connecting 4148 with seven pins.

Here’s a closer picture from the technical documentation: