GPS Speedometer module to Nixie tube display? - Page 1
Forum section: electronics / beginners

author: duckybiltindustries
author_rank: Newbie
timestamp: February 27, 2021, 03:12:10 pm
content: Hey guys, I'm a car guy with a lower intermediate understanding of electronics thanks to being a long time guitar player and general nerd who likes fixing/building things.I did search, the only thread that mentioned something like this was a 2017 thread with 0 replies lol.I have some IN12 tubes I bought forever ago and want to use them in conjunction with a GPS sending unit available on Jegs, this outputs a square wave signal (AC I believe, generally vehicle speed sensors are hall effect, this is meant to easily replace them, the listing is lacking literature) and can output 4k, 8k, or 16k pulses per mile.I've ascertained that I can use step up a converter(s) to power the (hopefully 3) tubes, they don't draw much current. What kind of circuit should I be thinking about to divide it out and switch pins on the nixie tubes? My knowledge essentially stops dead at IC's and micro-controllers, but I would think that the 30 (I guess probably 21, doubt I'm going over 199mph lol) pins that need to be switched to display all my digits would really warrant some micro-controller? Is there an IC I could use 3 or more of that would get me in the ballpark?I don't need hand holding strictly speaking, I can set up/wire and diagnose EFI systems with diagrams and pinouts, just lacking in the enginerding knowledge.If you point me in the right direction I'm happy to do the footwork, I just don't know where to begin.Any input is appreciated, If I can figure it out I think it would be a cool project to share with both the electronics and car communities.

author: Terry Bites
author_rank: Super Contributor
timestamp: February 28, 2021, 02:40:08 pm
content: https://www.eetimes.com/gps-driven-fpga-decoded-nixie-tube-speedometer-part-1/Luke's your man.

author: duckybiltindustries
author_rank: Newbie
timestamp: March 01, 2021, 08:35:22 am
content: Thank you! I'll read up!In the meantime I had found the K155/74141 IC with i/o tables (probably not the right term) and after some more research into Arduino, it seems it should switch fast enough to handle driving the digits, with the 3 IC's taking 4 inputs, I think a nano might be up to the task.I thought I could do some pulse per second math, give it some values, and it should be capable of interpolating well/fast enough to give me good output, +-5% would be acceptable.Not that I'm capable of writing functional code, but I'm sure with help from the googler I can dig up the info I need.Am I thinking about this the right way? Does any of this make sense? Just need to make sure I'm not stumbling blindly down the wrong path here lol, again, I'm a total noob at this stuff.I'll definitely read up still and see what he did, I'm just trying to learn how to fish here, as it were.Update: I read through Luke's posts and it gives me confidence that I'm sort of on the right track here.It does leave me with a few inferences/questions:Where he used a GPS module that output a digital datastream, I would think that having a dumb a/c pulse input like i plan to, would be much simpler to deal with in my application, is this reasonable/correct?Would there be a distinct advantage to using an FPGA or would you think that he used one because that's what he's most familiar with (being the FPGA expert) lol.Maybe Arduino wasn't as accessible then or didn't exist at all?My extremely superficial understanding is that FPGAs can run slightly faster, but I'm also under the impression that the Arduino is more than plenty fast for what I'm trying to do.If Arduino is simpler to use, i figure that's probably the route I ought to go haha.

author: Rerouter
author_rank: Super Contributor
timestamp: March 01, 2021, 09:12:41 am
content: To take a pulse source, you just need to count for the right amount of timefor say 8000 pulses per km, that works out to 133.33Hz at 60kmph, so if your gate time was 0.45 seconds, you could just directly show the count as the speed.That is the laziest way, but it ends up pretty close to the ideal update rate, for digital you don't want to update much faster than 3 times a second without a low pass filter of about 1 second.

author: duckybiltindustries
author_rank: Newbie
timestamp: March 04, 2021, 02:07:46 am
content: Thanks for the info, when you say I wouldn't want to update faster than .3 seconds, do you mean as in updating pulse count, output switching, or both?I was under the impression that both would be functions of the cpu clock speed, so orders of magnitude faster, obviously that's incorrect.Those constraints are fine either way, .3 seconds in or out is acceptable latency in this system.I'm just asking because I thought of the a/c pulse as an analog input (relative to the arduino) The ICs obviously require digital input, i do understand that much.Maybe using the pulse as a PWM signal could be helpful? Just spitballing.I'll look into gate times and familiarize myself more with how the arduino can process inputs because i don't think I have any questions right now that don't constitute hand holding lol. Thanks again for the advice, I've learned a lot already in this venture.

author: Rerouter
author_rank: Super Contributor
timestamp: March 04, 2021, 08:07:57 am
content: Update your display faster than that. Any faster and the human eye stuggles.Just feed the input into a comparitor setup for a 200mV hysteresis and a 150mV set point

author: IamSynthetiC
author_rank: Regular Contributor
timestamp: March 04, 2021, 01:28:37 pm
content: For controlling the nixie tubes you can also use an HV5122 or HV5222. It is a 32-bit high voltage shift register, that you can control with just 4 lines, it can fully control 3 nixie tubes and it canshiftat 8MHz. It is a bit expencive, but it is easly available and easy to control and code for.

author: Ian.M
author_rank: Super Contributor
timestamp: March 04, 2021, 02:22:44 pm
content: If you *want* GPS speed, if possible, use the raw serial output from the GPS module as theNMEA0183 RMC sentence*directly* reports the ground speed. If the GPS has satellites in view, (and has lock), it will report the speed in knots in a RMC sentence once a second. Its advisable to do a running average of the last three or so results as poor GPS reception (e.g in urban 'canyons', under overpasses, or under wet heavy foliage cover can degrade the signal sufficiently that the apparent position jumps badly enough for the receiver's Kalman filter to fail to smooth the reported speed.Once you've extracted and averaged the speed, multiply it by 1.15078 to get MPH and display it.However GPS speed is unreliable. GPS reception is extremely vulnerable to multi-path distortion and interference (e.g. a malfunctioning TV antennae booster amp can wipe out GPS reception over a 10 mile radius), and is extremely poor at penetrating ground, masonry or concrete, so a dropout is guaranteed in all except the shortest tunnels, and is frequent in hi-rise downtown areas. Use a real pulse output speed sensor linked to your road wheels, (preferably a non-driven axle), and ideally, auto-calibrate it against the GPS when there are sufficient satellites in view, and the vehicle is travelling in a straight line at a steady highway speed.