Posted on 18 May 2008
An AVR controller can be used as a counter, although it is a bit more involved than with a PIC. The reason is that a PIC (at least the 16F84) has an asynchronous counter input. This input will handle frequencies up to app. 40 MHz. AVR’s have a synchronous counter input which is sampled with the clock frequency, so it cannot measure frequencies over half the clock frequency. So, when using a 4 MHz clock, input frequencies must be lower than 2 MHz. Use 40% of the clock frequency to be on the safe side.[more]
Posted on 11 May 2008
The whole counter design is based on the PIC micro-controller 16F876A. The latter includes several peripherals and just a few of them are used in this project. The most important in this project are two internal, hardware counters/timers called TMR0 and TMR1. The TMR0 timer generates very precise interrupts every 100 microseconds (10kHz) from the 20MHz clock/reference. All required timings for the counter timebase are simply integer multiples of this basic period. [more]
Posted on 11 May 2008
The purpose of this project is to present a device that is useful and at the
same time demonstrate to the beginner many features involved in programming
the PIC. Some of the topics included are:
* Simple use of MPASM assembler
* Demonstration of use of timer 0 and the prescaler
* Use of length of instructions to set up timing delays
* Using interrupt routines
* Detection of switch closures including debouncing
* Saving and recovering data from the onboard EEPROM
[more]
Posted on 03 Apr 2008
Richard writes:While working on a project I came across the DDS chips from Analog Devices. Especially the AD9835 was very atractive to me because of its super simple handling and small size. Normaly you would use such a chip as a VFO or for other, similar functions but I decided to use it as a “Soundcard” for a project to do various digital RF modes with a PIC microcontroller. Some would say “I can do this with just the PIC and dont need a DDS chip”. That’s true but you would waste a lot of program memory for things like sine tables etc. With this solution you will have more memory available for your programs and you will get better signals than you could produce with just the PIC. The AD9835 comes in a very smal TSSOP housing. So to start developing I needed a more bigger, better to handle form of the AD9835. I packed it with a 50 MHz osciliator module and some parts needed for propper operation on a small PCB with two connectors with standard pin sizes. This simplifies the development enormous. You now can use your standard breadboard to design systems with the AD9835. [more]
Posted on 13 Feb 2008
The control pulse is defined by the width that represents “neutral,” or in the case of the motor controller the width that represents “stop,” and the change in width or delta that will yield full travel. A typical value for neutral on a Futaba R/C servo is 1520 uS.[more]
