Summary of Video Clock Superimposer using PIC16C711
This article describes a practical gadget that superimposes the current time ("HH MM SS") onto a video signal's bottom-right corner. Designed as a follow-up to a VCR Pong project, it is useful for home security systems. The device derives all timing signals, including the clock and timebase, directly from the incoming video. Consequently, if power or video is lost, the time display resets (e.g., to 12:00), which was acceptable for the intended security application.
Parts used in the Video Clock Superimposer:
- PIC16C711 microprocessor
- Incoming video signal source
- VCR (for recording)
- Home security system
- Parallax SPASM.EXE or Tech-Tools CVASM16.EXE (software tools)
- Device programmer (for INXH8M format object file)
About the Project
As a followup to my VCR Pong project, here is a gadget that is actually useful in the Real World! It superimposes the time of day, in “HH MM SS” format, in the bottom right-hand corner of an existing video signal. My friend Scott uses it with his home security system.
In keeping with the tradition of my previous hacks, I use few parts and lots of tricks. All timing signals, including the timebase for the time of day and the clock for the microprocessor, are derived from the incoming video signal. That means if you lose power, or lose video, it loses the time… but in this home security application, that didn’t matter. Lost power would mean the VCR stops recording and starts flashing 12:00 (1:00 during daylight savings).
Project Files
Here is the schematic, a parts list and circuit description, and most importantly the PIC source code.
The code uses the Parallax instruction syntax, so you’ll either need to use Parallax’s SPASM.EXE (available for free on Parallax’s web site) or Tech-Tools’s CVASM16.EXE (available for evaluation on Tech-Tools’s web site), or here is a preassembled object file, in INXH8M format, for use with any device programmer.
For more detail: Video Clock Superimposer using PIC16C711
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What does this gadget do?
It superimposes the time of day in HH MM SS format onto the bottom right-hand corner of an existing video signal. -
How are timing signals generated?
All timing signals, including the timebase and microprocessor clock, are derived from the incoming video signal. -
What happens if power is lost?
The device loses the time; in a home security application, the VCR stops recording and flashes 12:00 or 1:00 during daylight savings. -
Does losing video affect the time display?
Yes, because all timing signals are derived from the incoming video, losing video means the device loses the time. -
Which microprocessor is used in this project?
The project uses the PIC16C711 microprocessor. -
What software can be used to assemble the code?
You can use Parallax's SPASM.EXE or Tech-Tools's CVASM16.EXE, or use a preassembled object file in INXH8M format. -
Is this project suitable for real-world applications?
Yes, the author considers it a gadget that is actually useful in the Real World, such as with home security systems.
