As promised, today I will show you my latest addition to the super digital pressure gauge project - the "revolutionary" trailing analog bar graph with adjustable floor and ceiling. This feature provides a clear visualization of pressure spikes and troughs, and I, personally, think it's awesome! Before I direct you to the video of the prototype in action, let me explain how it works.
The AD7195 analog-to-digital converter reads the output of the Wika TTF-1 600-bar thin-film transducer at a rate of 150 settled conversions per second using ADC excitation of the transducer's bridge (to remove parasitic offsets).
On every sevenths read the MCU loops through the results of last seven conversions (stored in an array), defines the highest and the lowest value, and updates the right edge of the analog graph area with two corresponding vertical lines, scaled in accordance to the user-set floor and ceiling. The new lines are drawn in the order of appearance, and the existing lines are pushed to the left.
This gives the analog graph a refresh rate of 150/7 = 21 Hz and a moving trail, which, at the current display width of 128 pixels, allows for the registered spikes/dips to persist on the screen for three seconds, making their detection and evaluation much more convenient compared to the "classic" bar graph. The memory LCD from Sharp handles this refresh rate very well.
On every 28th read the MCU averages the result of the last 28 conversions, and updates the reading displayed on the screen in user-set units, which gives the main reading the refresh rate of 150/28 = 5 HZ, which is "just about right" (at least for my liking) - not too slow, and not too fast. The traditional re-settable maximum and minimum pressure records are also present and are displayed under the main reading (both at the same time).
Oh yes - I almost forgot. Since I am using the MCU of a Bluetooth module for all this "magic", the reading and the spikes are also streamed via Bluetooth.
As for the test, I was lucky to receive this old tipping valve for a re-seal the other day:
As soon as I saw that it had a simple ball for the relief poppet, I said: "This is it! Probably the nosiest valve I'll ever find!" so I gathered the development board and the pressure transducer in a basket, and brought this pressure measuring apparatus to the test bench!
Imagine turning up on a service call with a pressure gauge looking like that!
But, enough talk for today, here's the device in action, and I only ask one thing of you - please let me know what you think about this idea! I would love to hear your feedback!
