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home made quickshifter

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steven_191
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PostPosted: 17:26 - 17 Jan 2012    Post subject: home made quickshifter Reply with quote

inspired by nowhere.elysium's home made dash project i decided to have a play with the Arduino controller.

ive done a bit of messing around and already have various ideas for projects ill get stuck in with, probably all at the same time.

but heres the bike related one.

ive bought myself a £5 hand held digital scales. apparently from hong kong, which arrived today. I took it apart to have a nosey at it. The build of the strain gauge lever isnt what i expected but will benefit me as i can make the parts i need to fix into the gear linkage then bolt is in place. (you will see by the pictures)

so first things first. I gave it a 3v supply and hooked my work bag on it for a test. 10.77kg. so when i have it hooked up i can use that as a general reference. not that im interested in any specific weight value.

ill be taking whatever readings come out of the circuit map it to what i want then use that to pick a pressure at which to cut the ignition for a given amount of time then turn it back on.

my plan is to push onto the gear lever at a constant rate, and this will need a bit of trial and error to get it to a point where it comfortably moves the linkage, cuts the ignition, slots in the gear and turns the ignition back on. this will be in less than a second. maybe less than half a second. we'll wait and see.

the code side of this is very simple.

read the analogue data.
at a specified threshold switch the output
wait
switch the output back

ill also add a small screen in just so i can see the values to help with setting it up.

apparently the arduino can read an analogue input 10,000 times per second so this should be quick enough.

all i need to do is measure the current voltage used for the strain gauge. it runs on 3v so it may be that. and make sure i wire it up right

i have

I+
I-
E+
E-
on the wiring where its soldered to the board

i think e is excite meaning the value output but its connected to red and black which suggests power supply. the other cables,, green and white are what i would assume to be the output and these are labelled i.,

step one, get the digital scales

https://i1112.photobucket.com/albums/k493/steven_191/strain%20gauge%20quickshifter/IMG_1018.jpg

step two, take it to pieces

https://i1112.photobucket.com/albums/k493/steven_191/strain%20gauge%20quickshifter/IMG_1019.jpg

this is the strain gauge. it measures the force applied to the metal bar by its varying amount of 'stretch' on the sensor. (the sensor being a long thin bit of wire that changes resistance when stretched)

https://i1112.photobucket.com/albums/k493/steven_191/strain%20gauge%20quickshifter/IMG_1021.jpg
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CHR15
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PostPosted: 21:41 - 17 Jan 2012    Post subject: Reply with quote

looks very interesting.
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steven_191
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PostPosted: 16:30 - 19 Jan 2012    Post subject: Reply with quote

Been trying to do some calculations today to work out the best way to get a good reading from the gauge.

Looks like I might need something more sensitive but I'm not 100% on that yet.

I'm tempted to temporarily attach the gauge as it is and sense how much weight it records in order to pick another sensor if I do need to.

Otherwise the theory is thus

The arduino reads 1024 points across 5v. Meaning it senses a change every 49mV. Which seems small but you don't seem to get much deflection on the gauge. Or at least I'm yet to measure it. A lot of talk on the Internet of people using op amps to increase the voltage reading.

Either way I'm still to determine what the 4 wires are for. If its a single wire strain gauge there should be a pair of wires. Unless its a Wheatstone bridge set up which would make sense.

If I can decode the pcb I might even be able to use that as the input as its already set up to read the gauge. But that will likely be more effort

Also using your iPhone to write post means your garunteed that autocorrect will make you sound like moron.
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nowhere.elysium
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PostPosted: 17:07 - 19 Jan 2012    Post subject: Reply with quote

Can you post a couple of clear photos of the board, so we can try and figure out how it does what it does?

I'm not claiming any kind of expertise, but I'm guessing that it's mainly the display controller, with a fairly simple reset/calibrate function, and a set of fixed scales for measuring the weight.

Is a microswitch out of the question?
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steven_191
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PostPosted: 17:57 - 19 Jan 2012    Post subject: Reply with quote

a microswitch isnt accurate enough.

well the high quality chinese solder broke off almost instantly just by looking at it.

the strain gauge is no longer connected to the pcb Thumbs Up

Ive tested the voltage and resistance across a few wires before it few apart and the only change i saw was that the resistance went from around 1005ohms to 1008ohms. so not much really.

https://i1112.photobucket.com/albums/k493/steven_191/strain%20gauge%20quickshifter/IMG_1022.jpg

ive just soldered it back together and its working again. still havent found any details on how its supposed to work though.

there was a constant 2.2(ish)volts on the red/black so that could be the supply.
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lllN30lll
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PostPosted: 18:30 - 19 Jan 2012    Post subject: Reply with quote

Could you not do it this way?

https://www.zx-10r.net/forum/showthread.php?t=110223

https://i12.photobucket.com/albums/a244/3A-Sgt-Reaper/678A0247.jpg
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CHR15
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PostPosted: 21:25 - 19 Jan 2012    Post subject: Reply with quote

oh hi shervin.
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steven_191
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PostPosted: 22:02 - 19 Jan 2012    Post subject: Reply with quote

i could do it that way but its a bit pants.

if i do it with the controller and the strain gauge i can set it up more accurately

also im thinking, i wont want it on all the time and at different engine speeds it may need longer or shorter times to slot into gear because the engine will spin at a different speeds.,

so the code can include that, give the ignition a bit more time to change at a lower speed or even only change above x rpm.

otherwise ill need a switch that i have to flick everytime i want it on or off.

of course ill need to measure the engine speed but that can be done without too much trouble.
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steven_191
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PostPosted: 13:03 - 20 Jan 2012    Post subject: Reply with quote

i measured a 5mV deflection!!!

yes i know, its shit. Thats 1 step change on the arduino lol.

it doesnt matter too much know. ill be buying some low voltage amplifiers (LM386), which appear to do what i need and are cheap so dont mind having a punt to see how well they work.

still might need a more sensitive gauge though. ideally i want one that already stuck to a bit of metal. not 100% on the range yet. the one i got was the largest range for the cheapest price so thought it was a good place to start.
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nowhere.elysium
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PostPosted: 13:36 - 20 Jan 2012    Post subject: Reply with quote

I can't help but think that we should join forces, you know. Combine my dash, with your quickshifter, and work out a bunch of other trick bits for bikes, then just package the whole thing up as a complete trackday/tart-up system.

Having said that, I'm clearly just trying to poach your electronics expertise Laughing
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steven_191
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PostPosted: 16:38 - 20 Jan 2012    Post subject: Reply with quote

im by no means an expert at this stuff. I did some electronics at school which was something like 9 years ago now and and have been getting a bit more involved in the last month through the arduino and some in my job as we get more involved with parts.

the rest is just research and shit i remember. for example, i have an old box of tricks from school. i just raided it and found an op amp which im trying to wire up.

im pretty sure it worked once but havent seemed to get any decent values since one of the wires broke. this may have fucked up the chip lol.

but anyway, once this lot is done ill send you the details and im sure you can join it up to your dash project easy enough. im using 1 analogue input and 1 digital output. plus another digital input if i want to use this speed compensating idea, but you already have that.

probably just going to wait for the voltage amps now and see how they go.
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nowhere.elysium
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PostPosted: 16:47 - 20 Jan 2012    Post subject: Reply with quote

steven_191 wrote:
but anyway, once this lot is done ill send you the details and im sure you can join it up to your dash project easy enough. im using 1 analogue input and 1 digital output. plus another digital input if i want to use this speed compensating idea, but you already have that.


Cool. Doesn't mean I'm not going to pick your brains periodically, though, along with those of the other main contributors in my thread. Very Happy

I'm going to be banging heads together with my Dad this weekend, to try and plan out the coding that'll be required for the big bastard version of the dash, along with the I2C coordination and hardware integration.

I'm reckoning on designing and planning out the fullest spec possible, and then trying to make it as completely modular as I can. That way, it's just a matter of whether or not you want the function - if you want it, plug it in; if you don't, then don't.

Once I've got something to show, I'll pm it to you.
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steven_191
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PostPosted: 17:59 - 20 Jan 2012    Post subject: Reply with quote

the only trouble with doing it that way is that whatever wants to be displayed thats not plugged in wont be displayed correctly so you might have odd numbers on the screen.

and if that is the case you will need to compensate with some sort of digital input built into the 'plug' that you may of may not be using and this could turn that area of the dash on or off when it senses its plugged in Thumbs Up

also think my op amp is buggered. it measures the different between the two inputs so if you have both inputs from the same source the output =0v. except it doesnt. its 1.68v or something. i connected a potentiometer to one line and the output goes from 5v to 1.6 with nothing in between. definately fucked!!!
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nowhere.elysium
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PostPosted: 18:14 - 20 Jan 2012    Post subject: Reply with quote

steven_191 wrote:
the only trouble with doing it that way is that whatever wants to be displayed thats not plugged in wont be displayed correctly so you might have odd numbers on the screen.

Nah - I can just put in a bit of code that polls the external device - if there's nothing plugged in, I should be able to account for that.

steven_191 wrote:

and if that is the case you will need to compensate with some sort of digital input built into the 'plug' that you may of may not be using and this could turn that area of the dash on or off when it senses its plugged in Thumbs Up

I can write functions for different screen layouts, depending on whether things are present or not. A series of if/then functions will take care of that when the thing boots up.
steven_191 wrote:

also think my op amp is buggered. it measures the different between the two inputs so if you have both inputs from the same source the output =0v. except it doesnt. its 1.68v or something. i connected a potentiometer to one line and the output goes from 5v to 1.6 with nothing in between. definately fucked!!!

That sucks. I'm going to be putting together a large(ish) farnell order at the end of the month, if you want to chuck a few parts on my list, just pm them over.
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Codemonkey
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PostPosted: 19:31 - 20 Jan 2012    Post subject: Reply with quote

steven_191 wrote:
also think my op amp is buggered. it measures the different between the two inputs so if you have both inputs from the same source the output =0v. except it doesnt. its 1.68v or something. i connected a potentiometer to one line and the output goes from 5v to 1.6 with nothing in between. definately fucked!!!


What Op-Amp is it ? Have you biased it correctly and set a feedback resistor ?

I'm not sure how much you know about them so forgive me if I'm teaching you to suck eggs, but unless they've got all the biasing & feedback components around them, they are useless. The gain is typically >1000, possible >1000000 so even a tiny change in input results in a full rail to rail swing on the output. Also, they tend to require dual rail PSU, i.e. +V, 0V and -V. On a single supply system, connecting the inputs together will probably result in the output going to half the supply voltage (the Op-Amp's mid level).
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steven_191
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PostPosted: 22:42 - 20 Jan 2012    Post subject: Reply with quote

Well I've been having a play with it. I connected a resistor back from the output to one of the inputs. I did read a bit about the biasing but I didn't think that applied. I thought I could set it up so that the differential in the two inputs is what gets amplified.

i set it up as per this

https://www.daycounter.com/Calculators/Op-Amp/Op-Amp-Voltage-Calculator.phtml

and used the calculator to work out my resistors.

the op amp im using is a UA741
https://www.datasheetcatalog.org/datasheet/SGSThomsonMicroelectronics/mXssuwx.pdf

and the one i will be getting is
https://www.ti.com/lit/ds/symlink/lm386.pdf

although this isnt an op amp like the UA741.

also i did try having a capacitor between V+ and ground and lastly i was running this from a 9v battery through a 5v+ regulator. so the actually circuit was all 5v+ and ground. no negative voltage.

if you know how i need to set it up that would be helpful. cheers

edit;

i measured the volt out from each pin of the strain gauge to ground and they were both the same even under stress. but when testing between the pins i get around 5mV deflection. i need to amplify!!!!
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Codemonkey
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PostPosted: 21:11 - 21 Jan 2012    Post subject: Reply with quote

You might want to read this

Also, there is a useful program from Linear Technology that will allow you to simulate these things before wasting time building them. Its called LTspice and you can download it here
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steven_191
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PostPosted: 19:30 - 23 Jan 2012    Post subject: Reply with quote

I got some LM386 chips but as yet haven't got them working. I'm getting voltage out but it's not changing with the strain gauge.

I've wired them up according to Texas instruments schematics for -20 gain and -200 gain with the only difference being I don't have exactly the right capacitors. I'm rounding to the nearest eg. 220mf instead of 250mf and 0.33mf instead of 0.05mf and 10mf. Similar with the resistors really.

Not sure how much this effects things really. ???
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Codemonkey
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PostPosted: 08:04 - 24 Jan 2012    Post subject: Reply with quote

It would help if you could post a schematic of what you have. You could use that LTSpice application to draw one then post a screenshot or something ?

As for component values, well it just depends what components!

Really you'd be better off with a single rail Op-Amp. The thing you are using is an audio amplifier and the schematics shown in the datasheets (this one at least https://www.ti.com/lit/ds/symlink/lm386.pdf) are all for amplification of ac signals. You are trying to amplify a dc signal.

The datasheet attached shows a single supply (5V) strain guage amplifier on page 11 (Figure 16).
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steven_191
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PostPosted: 17:58 - 24 Jan 2012    Post subject: Reply with quote

well thats the datasheet i have and ive tried the circuits with varying gains.

i just seem to get a constant output. Ive connected a pot to the input in order to have a bigger range on the output but its not doing much.

I have a 220mf cap in place of the 250mf and a 0.1mf in place of the 0.05mf.

I have some other chips i can try but if ive already killed one i want to be a bit more sure that i wont do it again.
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Codemonkey
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PostPosted: 19:24 - 24 Jan 2012    Post subject: Reply with quote

It would be really helpful if you could post a pic of your complete circuit schematic. You could have simply made an error in how you have everything connected but without being able to see things I'm running out of suggestions!

LTSpice can really help you here, its not hard to use, has "models" for many op amps already, and can be used to test your circuit without actually building it or potentially damaging more bits. Alternatively, you could just use it as a simple cad package to draw the schematic.

Also, which datasheet are you referring to, the texas instruments one for the audio amp I linked to, or the NXP/Philips one for the Op-Amp I attached ?
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steven_191
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PostPosted: 21:47 - 24 Jan 2012    Post subject: Reply with quote

https://i1112.photobucket.com/albums/k493/steven_191/strain%20gauge%20quickshifter/4bcf757c.jpg


i was talking about the texas instruments pdf. the only thing this is currently missing is where the output is going. I normally connect a lead and clip the volt meter onto it. I also tried a buzzer so that i could ground the other end and make sure it wasnt because of an open circuit. but it was a 6v buzzer and only had about 4.5v coming out. buzzed ones very quickly then nothing. I also tried a small piezo element but that has a slight click when voltage is applied but no sound.
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nowhere.elysium
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PostPosted: 11:40 - 25 Jan 2012    Post subject: Reply with quote

steven_191 wrote:



i was talking about the texas instruments pdf. the only thing this is currently missing is where the output is going. I normally connect a lead and clip the volt meter onto it. I also tried a buzzer so that i could ground the other end and make sure it wasnt because of an open circuit. but it was a 6v buzzer and only had about 4.5v coming out. buzzed ones very quickly then nothing. I also tried a small piezo element but that has a slight click when voltage is applied but no sound.


I'd use an LED instead of a buzzer - you get a more definite response, and they're designed for 5v instead of 6v, which will help.
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steven_191
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PostPosted: 13:25 - 25 Jan 2012    Post subject: Reply with quote

Yeah I tried an led too. It lit up but didn't vary. I'll probably try another chip and see what happens. Can you see any problems with how I've wired the breadboard?
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nowhere.elysium
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PostPosted: 15:26 - 25 Jan 2012    Post subject: Reply with quote

OK - firstly, Codemonkey's advice of using spice is good. Take heed of it.
Secondly, from what I can see, this is how you've wired this up:

https://farm8.staticflickr.com/7165/6760450911_c3f8dd9022.jpg

I've just noticed (after running your image through a massive zoom factor) that I've put the notch at the wrong end of the chip.
However, would it not make sense to isolate the input from the variable resistor from the output from the chip?
If you could give us a more accurate diagram of what you've got, it'd help. I'm far from knowing what I'm on about when it comes to electronics, but it's easier to read diagrams than to decipher someone else's breadboard Laughing

As an afterthought; does a negative voltage input have to be from a separate inverted source, or can it just be hooked into ground? I've never been sure.
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