StroboLPscope is a OSHW project developed for education purpose @LAB2104. The projects implements controller for driving bright leds with quartz constant frequency and duration for both disc speeds of 33/45 rpm and 78 rpm (revolutions per minute). A stroboscope also known as a strobe, is an instrument used to make a cyclically moving object appear to be slow-moving, or stationary. It consists of either a rotating disk with slots or holes or a lamp such as a flashtube which produces brief repetitive flashes of light. Usually the rate of the stroboscope is adjustable to different frequencies. When a rotating or vibrating object is observed with the stroboscope at its vibration frequency (or a submultiple of it), it appears stationary. Thus stroboscopes are also used to measure frequency. The principle is used for the study of rotating, reciprocating, oscillating or vibrating objects. Machine parts and vibrating strings are common examples. A stroboscope used to set the ignition timing of internal combustion engines is called a timing light.
The current project uses slots in disc, which are usually calculated for frequency of the light of 50 Hz. The slots are different for the two speeds of 33 rpm and 45 rpm. Usually the 78 rpm is not supported as slots because it is obsolete rotating speed. But still there is many records on 78 rpm. This project contains switch, which enables the use of the current disc slots for the low speeds to implement the stroboscope effect for the 78 rpm. The stroboscope generates constant frequency of 100Hz (which is the second harmonic of the common used 50Hz) or 117Hz (which enables the stroboscope effect on 78 rpm with the slots for the 33 rpm) with duty cycle of 10%. You can find more details about the software part and the schematics at the project archive: stroboscope (project files)
The software is based on the Microchip’s assembler language (MPASM). Development environment (IDE) is the MPLAB software, which is free for use. We use the programmers, developed by local hardware vendor Olimex, but you can use any standard tools for programming the chip, like PICkit3, etc. You can also download the PowerPoint file, described the project: stroboscope (PowerPoint)
Hardware uses a single chip micro-controller (PIC16F84-04) with embedded 8-bit timer (TMR0). The instruction frequency is based on HS external quartz crystal with frequency of 1.8432 MHz. That is why the used controller is marked with signature -04 (this limits the chip up to 4 MHz instruction executing speed). You can use any general PIC16F84 controller without any mods in the source and hex files.
Soon we’ll add more detailed explanation of the source code, which will be useful if you plant to use this project as a base for different turntable models and frequency sets.
There is another interesting stroboscope project done by Leonid Ivanovitch. It is done using ATtiny12L controller and has two advantages:
– the current consumption is constant, there is no interference on the supply circuit;
– for the frequency generation used DDS principle, with any quartz any output frequency is possible with good accuracy;
You can find more information of the Leonid’s project in the following link: http://leoniv.livejournal.com/252528.html
Source code and the circuit diagrams can be found by clicking here.