Hi all,
I've been working on this design. The idea is to use Dekatrons to display the value of an input signal. It will necessarily update quickly, so it may be interesting to use it to view varying voltages. It will use the persistence of vision effect while incrementing a Dekatron (slowly for cathodes with associated values below input signal level, quickly for those above). It uses a DAC formed by the conduction of the cathodes as an input to a comparator which will disable a clock divider which feeds a finite state machine which produces the sequences required to increment the Dekatron. The clock divider w/ enable is there so that while the dekatron is working on "turning on" digits below the input signal threshold, it will do so slowly (Appears brighter). And while above, quickly (Appears dim).
I know this could be done fairly easily using a microcontroller, but I'm pretty new to electronics and wanted to challenge myself to produce a nice design with mostly discrete parts.
So far, I've done the high-level functional design of the voltmeter; and simulated it almost entirely in LTSpice. Now, I'm beginning to pick components and create detailed schematics.
I've attached some pictures which show some detail through the design process.
The block diagram is from before I realized that the FSM needs the comparator output as an input, and that it also needs to control the clock divider enable line. This is because a random cathode will conduct when Dekatrons are initially powered up. The FSM will 'zero' the Dekatron by counting up quickly until the zeroth (top) digit of is conducting.
I even simulated a Dekatron, which included making an FSM to decode the gate pulses delivered by the gate-sequencing FSM, feeding pulses output by this into a decade counter, then a decoder which enables a 450V source in series with 790k resistors (the anode current-limiting resistor) through to each individual cathode pin.
I need to determine what clock frequency and divider ratios I will use. I think I will do this with a microcontroller, emulating the behavior of the circuit, since it's easier to adjust values there.
In the attachment file named "overall.png", a simulation of the full operation of the circuit is shown. The magnitude at any time on the DAC waveform shows effectively which digit of the Dekatron is lit up.
I am interested in hearing feedback about the design, especially if something blatantly won't work in the real world
