Digital Dash project

paul1950

New Member
Does anyone know where the site for a picaxe tachometer and digital dash project has gone to ?
This project was fitted to a race car and details were at www.tach.rex-deb.net
This site has disappeared.
Or does anyone have a copy of this project ?
Regards, Paul
 

Shack

Member
Digital Dash



I finished the project but have not updated anything because I am in the tuning phase of the car with the new engine and turbo.

I finished the GPS timing system with Jeremy using the 28x1 Picaxe and added a turbocharger to the car but that stuff is not posted. It has only been to the track once and scheduled to go back in a month.

The turbo project is here:
Turbo

The GPS system is here:
GPS Lap Timer
 

paul1950

New Member
Tachometer project

Thank you for the tacho link.
Unfortunately I cannot open the Bill of Materials to get a list of parts.
Regards, Paul
 

paul1950

New Member
Digital dash parts supplied

I cannot find a supplier for some of the parts for the digital dash project in Australia. (4 segment CC LED and driver, FET's)
Can you advise me of a supplier in the UK (web address if possible)
 

Shack

Member
I cannot find a supplier for some of the parts for the digital dash project in Australia. (4 segment CC LED and driver, FET's)
Can you advise me of a supplier in the UK (web address if possible)
You will probably need to make a new design because I don't think you will be able to find the display. It is a Lumex unit and internally multiplexed. You will need 4 single digit seven segment displays (CC) instead to connect to the MAX 7219. The code will be the same.

The larger FET is to drive a special motor and you do not need it. If you just want just the shift light any small FET will work with the shown circuit (TO92) and it does not need to be the VN10 (I just like them). In a re-design you can use a NPN transistor with a couple of resistors added. The FET turns on with voltage but the transistor needs current so it requires the additional components.

The tach input ... you can use about any PNP transistor there.
 

paul1950

New Member
After much searching, I have found a suplier who has a MAX 7219 display driver.
They also have 4 x 7-segment LED displays but I do not know which brand. Hoping that they are compatible.

My project is to use an optical sensor to measure RPM.
A large flywheel on the engine has 4 holes in it and I intend to use an LDR to sense the flashes of light as it rotates.
The sample input circuits show the LDR connected directly to the Picaxe with a resistor to ground. Should I do this or connect thru a flip-flop first ?

As there will be 4 pulses per rev. So will set the selector switch on the board to the 4 cylinder setting.
 

Dippy

Moderator
Best that you check LDR data sheets for response time. Note response times change depending on light levels too. I'd be surprised if it was fast enough. Check out Phototransistors.
 

Shack

Member
After much searching, I have found a suplier who has a MAX 7219 display driver.
They also have 4 x 7-segment LED displays but I do not know which brand. Hoping that they are compatible.

My project is to use an optical sensor to measure RPM.
A large flywheel on the engine has 4 holes in it and I intend to use an LDR to sense the flashes of light as it rotates.
The sample input circuits show the LDR connected directly to the Picaxe with a resistor to ground. Should I do this or connect thru a flip-flop first ?

As there will be 4 pulses per rev. So will set the selector switch on the board to the 4 cylinder setting.
The display you are looking at probably will not work but I will post a new schematic for you that will work. You need 4 individual 7 segment displays. It is quite unlikely that the unit you found will be wired the same internally as the Lumex unit so look at the data sheets carefully. You also need very bright super red’s.

Unless you have a good reason, the LDR is probably not a good idea. You can derive a tach signal from any ignition source. If it is an engine it has one. There is a tach input link on the website also.

If you use the flip-flop you need to configure it as a divide by 2. Then the code will be for 2 cylinders as written.

If this is for a fixed application the dip switch to select cylinders isn't necessary. You can just set it in the code for the correct value. This removes the resistors and switch. You also need to #rem out the selection in the code and substitute you value there after the ADC read.

Here are two files you can view.

This is how to connect the MAX 7219 with the 4 individual displays. They are quire common, but check the data sheets to be sure they are pin-for-pin compatible with the LiteOn one I used or do a new schematic. They are also inexpensive so get 1 extra (for a mistake ..lol)... they must be CC.
MAX 7219 Connection

Here is a sheet I did for the race cars on the tach inputs:
Tach Circuits
 

paul1950

New Member
Thanks for all of the feedback. I appreciate the help which you have given. I an relatively new to electronics and need all the help that I can get.
The LED module that I have found has very similar specs to the Lumex brand, so will keep my fingers crossed that it works. Otherwise will use 4 x single units.
Unfortunately I cannot connect to a tach signal as there are no electrics on the engine. It is a steam powered traction engine built by John Fowler (UK) in 1927. (see photo).
The 3' dia flywheel on the end op the crankshaft has 4 x hand holes for manually turning the crank.
I had intended to use an LDR to sense flashes of light passing thru these holes as it turned. Max speed of the engine is only 600 rpm.
Is there a better solution than using LDR's ?
Regards, Paul


traction engine 2.jpg
 
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eclectic

Moderator
What a magnificent beast!

As a total aside, you could rig up a dynamo and really have
a steam powered Picaxe!

e.
 

paul1950

New Member
A steam powered picaxe is in the pipeline. We intend to run a generator for lighting. In fact early "Carniaval" engines had large generators and were used by circus troups to light their tents and side-shows.

This is a copy of the data sheet for the LED module that I have found. It seems to be similar to the Lumex brand.
View attachment LED Display - 7FR5641AS.pdf
 
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Dippy

Moderator
Do the maths Paul. Your holes in your flywheel are Xcm big on a radius of Ycm. It does 600RPM max(?). So how long would a 'beam' of light be passing through the holes. Piece of cake.
If it's less than tens of milliseconds then forget LDRs.

Like I said before look at phototransistors. Much faster. Much squarer. Obviously using holes you'll need a bracket/fitting each side and wires - yuk. You could go a photo reflective approach and little glue-on reflectors on your flywheel in much more convenient places as far as sensor mounting is concerned.
Could even be magnetic rather than optical.

Have a good long think. But nice project.
 

paul1950

New Member
I only need to mount a sensor behind the flywheel, out of sight.
The engine is only used in daytime and sunlight used for illuminating the sensor.
From comments that I have received, it looks a phototransister is the way to go.
Does anyone have a typical input circuit ?
Have also thought about magnetic or hall effect sensors.
 
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Dippy

Moderator
I think a lot of suggestions may depend on your flywheel. How much does it wobble? I mean if you had a sensor 5mm to one side of flywheel face would it clout it?

I reckon you'd find magnetic/hall easier personally. Just my opinion. Sensors/switches are piddly little things and cost anywhere between 80p to £3. Probably even cheaper on Ebay but I wouldn't waste my time with them after the recent experience with my tin opener.
 

eclectic

Moderator
Paul.
Following Dippy's suggestion, and the caveats regarding wheel-wobble;

How about some initial testing using a cheap Bike-computer?

They can be bought for less than a fiver, and you'll have a
magnet, reedswitch and display to play with.
I've seen them in supermarkets and the "e" place.

Obviously, you'll need to calibrate it and perhaps change the magnet.

And if it doesn't work? Give it to someone who's got a bike.

e.
 

paul1950

New Member
Because of flywheel has a lot of wobble I cannot mount a sensor close to it.
Have thought about a bike tacho but the display screen is too small and pick-up has to be close to the wheel (wobble problem)
Have also tried an opotical tacho which reflects light off reflective tape. This worked OK while inside a building but not outside in daylight.

The engine is only used in daytime hours, so I would like to use sunlight as the light source and mount a pick-up behind the flywheel. This area behind the wheel is in shadow.
Plan to mount the photo transistor inside a piece of tube which will shield it from any side light. This could be mounted 50mm or 100mm behind the flywheel and will not be hit by the wheel wobble.
Now just have to build it.

Also looking at using a photo diode. Has anyone used one of these and has a typical circuit ?


Wheel.JPG
 
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Dippy

Moderator
50mm to 100mm - JEEZ, that's what I call wobble.
Has anyone done any testing using a Hall Effect switch sensor and a v.powerful little magnet to get a couple of inches range. I'm sure it can be done.

Many op-amp data sheets give simple exampls of how to use photodiodes.
This one is an example:-
http://www.farnell.com/datasheets/64561.pdf

Figures 3-9 and 3-10 on page 13. Can't get much easier.

With your method of using ambient light what happens if the sun light comes in from the other side?

And photodiodes are very sensitive to IR light unless you get a filtered type. You will have reflections on inside of tube giving funny figures. You may need to baffle the tube and you may need to run it through a monostable before PICAXE.

But I agree a photodiode is better than photo/tr.

May I ask, why did you think about using a photodiode?
 

paul1950

New Member
Dippy,
The wobble on the edge of the flywheel is probably less than 10mm but there is also a small amount of side-play (it was built in 1927 after all).
By saying 100mm I meant that the sensor could be mounted way back from the wheel, out of harms way.
Ambient light comes in from all directions and hopefully is bright enough to trigger the sensor at all times.
Did not know about photo diodes, but when I went down to my local parts supplier for a photo transistor, he gave me a diode by mistake.
The sensor will be mounted remotely from the circuit board and running 2 wires instead of 3 should be easier. I plan to use shielded co-axial cable just in case stray nasties are picked up by the long extension lead.
Regards, Paul
 

Shack

Member
Probably looking at the wrong location and over complicating the issue.

There should be a better location for a simple micro switch to act as a direct counter in a timed loop to derive the RPM.

Look where the flywheel is linked to the drive.
 
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