Immediately, anticipating the bewilderment of readers, I will make a reservation: the use of the device is purely special. The need arose to indicate parts of images on projections of a large difference in brightness, for example, the projection of stars in a planetarium and the projection of a presentation on the same dome. Lecturers, so that the trace of the pointer does not clog the projection of the starry sky (even when using the pointer with a minimum power of 1-5mW), shone through the sleeve cuff or select specially “dead” batteries. When explaining the projection of graphs or other objects on the projection of the presentation on the (screen) dome, the pointer was used without shading. These methods seemed to me blatantly not modern, so the idea was born of attenuating the intensity of the laser pointer spot by electronic means.
The principle of controlling the brightness was chosen pulse-width, since laser diodes do not have a wide dynamic characteristic and current control would be difficult.
The first option was based on a logic circuit generator. The regulating element was a variable resistor, so there were two controls for the pointer: the power button and the resistor wheel. Therefore, the body of the pointer had to be done. Suitable was made from a suction casing. The advantages of operating such a pointer are its intuitive ease of operation, but it is not very convenient to set the required brightness: you need to turn the knob with the power button pressed at the same time.
An approximate scheme of a laser pointer with adjustable. First option.
Appearance:
The next option was a pointer with minimal mechanical alterations. The minimalist option is with one button, low power, for common AA batteries (2 pieces).
The appearance of the prototype.
Provided that mechanical alterations should be minimal, the question arose about the brightness control. It was possible to consider a resistor, but the introduction of a mechanical control into the design, its integration into the existing design would complicate the design, so it was decided to dispense with the only control button and turn on / off and the brightness of the glow. This option, given the very modest size of the prototype, requires a transition to a fundamentally new circuitry. As e The ATTiny13A-SSU microcontroller, which has the appropriate dimensions and software and power capabilities, was chosen for the fillings.
Using breadboard and when using Arduino UNO as a programmer was developed in the Arduino IDE environment and the pointer control algorithm was flashed into the microcontroller. Firmware listing in the application (listing.zip).
To separate the on / off and brightness control functions, a temporary method of signal separation was applied: short press - on / off, long press - brightness control. With a long press, the brightness changes cyclically from minimum to maximum according to the cubic dependence (in this case, it is an approximation of the exponential dependence) for visual linearity. The brightness at which the button is released becomes current. And with subsequent short presses, on / off is performed at this brightness level. To protect against forgetfulness, the included pointer, if there were no influences, “falls asleep” after 5 minutes (current consumption is several milliamps), while the level of the set brightness is remembered and restored the next time it is turned on (by pressing the button). The disadvantage of the system is the unusual control of the pointer.
The stitched controller is mounted on the pointer driver board, as if intended for this. For normal operation of the laser diode with the same operating current, it is necessary to replace the SMD resistor with a smaller one - 20 Ohms. It is also necessary to cut the conductor immediately after the resistor, with which it is connected to the button contact.
Laser pointer scheme. The second option.
Pointer board with installed microcontroller.
Execution options - nothing has changed outwardly.
Several copies were made, the flight is normal, only lecturers can hardly master the unusual use, unfortunately.