Universal PI Micro

[johnno]

Re Atmega168

Hello Again ..what price are we looking at?
Thanks
johnno

[bugwhiskers]

Hi johnno,

Thanks for your interest in the project.
The boards will be shipped with the micro pre-programmed.
Source and HEX code (everything you need) will be included.
The board will have a 6 pin programming header for those who want to try their hand at making changes. However, the whole thing is being designed so that all the changes you need to make can be done with the front panel knobs and button.

The timing section of most PI's is very similar, this project supplies that and more, like a MOSFET driver, a +5(over battery +) charge pump, LCD screen, "G" sensor and audio.

regards
bugwhiskers

[johnno]

great post!

The software required to program the atmega168, is this to be public domain?,or do we try ourselves..(Ihave no programming experience.only BASIC).
Thanks
johnno

[bugwhiskers]

UPIM audio

One of the major problems with audio in a PI circuit is at the threshold of detection the change in output from the amplifying stages is very small. If the audio is a rising pitch with rising signal strength the change with small or distant targets will hardly be noticable. The use of an anolgue meter does help but clearly a better method is required.

In the preliminary overview posted earlier you will see a box labelled "Audio".
The audio will be generated by the micro's internal PWM. The way this works is fairly simple. The voltage from the final amplifier stage is read by the AtoD and converted into a number from 0 to 1023 (10 bit resolution). That number is fed to the PWM and the output pin produces a signal the frequency of which is dependant on the number it is fed.

Clearly, if the signal input changes from 0 to 1 as it will at the threshold of detection then even Mozart would have trouble hearing the change.

A way around this problem is at the threshold of detection AtoD read = 0 a steady tone (maybe 500Hz) is heard pulsed on and off at .25 Hz. If the AtoD goes to 1 then the rate of the pulsing of the steady tone is doubled, now the change is very discernable. After about 8 doublings of the pulsing of the tone the PWM would go to normal rising pitch to indicate target strength.

regards
bugwhiskers

[bugwhiskers]

Layout of adjustment screen

The attached .pdf (which needs to be rotated right, clockwise) shows the intended layout for the adjustment screen. All the delays and widths will be adjustable from .5 to 512 microseconds. The CT (cycle time) will be shown in Hertz and the maximum frequency is dependant on the total of all the other widths and delays and internal processor tasks (driving screen, reading AtoD inputs etc)

A suggestion from bbsailor was to have the "G" force sensor instigate changes in sampling dependant on sweep speed. No signal from the "G" sensor after a set period could also turn off the TX pulse to conserve battery power.

Additional 4094's on the SPI line could be added to provide extra digital outputs or drive a DAC to produce perhaps changes in offsets or gains.


regards
bugwhiskers

[bugwhiskers]

The attached .pdf shows a preliminary detailed overview of a stand alone circuit board that will greatly aid those conducting experiments in PI metal detection. It can drive PI's like the Hammerhead, Gary's PI, Goldscan4 etc.

There are 3 outputs to drive analogue switches or JFET's, most PI's only use 2. The delay between each output and the sample width are adjustable from 0.5uS to 512uS and are displayed simultaneously on a 16 character * 2 line screen. The screen will have another page to show a digital readout and bar graph of the final stage signal strength.

Two pots and a pushbutton serve to navigate around the adjustments and displays. Turning the "mode" pot will cause stepping between various screen pages and variables. The "adjust" pot causes the variable to be changed with the "accept" button storing the new value. Adjustments will be live, so the user has instant feedback. There will be provision for storing (retained with power off) 16 sets of all variables into EEPROM.

Feedback and suggestions for additions are very welcome and the sooner the better as I am in the process of laying out the board.

To complicate things, I have finally bitten the bullet and started to learn to use "Eagle" light PCB program after using a DOS version of PROTEL since 1990.

regards
bugwhiskers