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MCU displays multiple chart or scope timing ticks

28 Mar 2016  | William Grill

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When I was using a 10bit DI-184 module from Dataq to monitor and display vibration-sensor data, I learned that, although the chart displays a time index, this time reference is not visible in the saved file. You can add time ticks, representing seconds or minutes, to a chart graphic by using a simple and inexpensive crystal-based microcontroller to generate a sequence of tags on a dedicated chart channel. The figure shows a small, eight-pin 12F508 microcontroller from Microchip Technology that provides multiple timing ticks. The listing, the microcontroller's program, offers four timing sequences. You can select a timing sequence by strapping pins 4 and 6 (table).


Figure: An 8bit microcontroller with output pins 5 and 7 configured as a 2bit DAC provides precise timing ticks to annotate captured data.


Figure: Timing sequences.


The 4MHz crystal maintains a solid instruction-timing reference, and equalised coded branches in the listing maintain accurate timing ticks. You can also configure the 12F508 with an internal, 4MHz RC oscillator. You base the coded loops on a sequence of exactly 25 instructions, and they provide a fundamental, base-reference loop that is exactly 100 instructions. A 16bit register counter serves as the multiplier to produce the base timing. For use with scopes, you can recode the listingwith minor changes to use 50 instructions or a 50-µsec base-timing-tick minimum. The 8bit registers in the equalised loop provide multipliers to produce the additionally tiered output. The microcontroller uses two output pins, 5 and 7, as a pseudo 2bit DAC. This configuration generates one of four voltage levels for timing ticks that display continuously, and you can record them along with application data.


About the author
William Grill contributed this article.


This article is a Design Idea selected for re-publication by the editors. It was first published on May 1, 2008 in EDN.com.




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