Home made tach super fast and cheap !

A fun project is coming to time to test..
i dont know how many of you guys would be interested in this sort of thing but thot i would put it out here for suggestions on what users would want from a saw tach..
this could be available from a complete DIY kit to put together to a stuffed board ready to solder..
as it is now sampling rate is set at 250ms , i can program it to sample up to 100 times a second but the led's wont keep up i think..
so far it tests to within 10 rpm's at 20k rpm's..
when i get the board back next week i will be testing it and burning the chip with diff codes to try out diff functions..
will be trying a programable decimal point for closer readout as the first digit,a "one" is not really needed in a saw tach..but another thot is the last digit only represent 9 rpm's..so what should it be ??
having only four digits keeps it a LOT cheaper and a lot less parts..
this beta version has full sized electolytic caps that will be changed to SMT type,will even make board smaller..
color of led readout ? did blue because i like it but red is cheaper..
this beta board is adjustable with a voltage input to calibrate to get the accuracy so close..
what would be an acceptable accuracy amount to be able to make it smaller and cheaper ??
also able do do 4 stroke engines but i think i will do away with that for now..
well,,i guess thats enuf info for now to get some responses so here are some pix.. notice the board is not trimmed so it looks big and using full sized transistors,,if less accuracy was acceptable the crystal and VC could be eliminated and the board could be 1/2 the size..
oopss, am i going overboard here ??
then give me input !!
one pic shows the board reading out,results from the signal generator in the other pic..pretty DARN accurate !
one more thing..i am not a sponser..i am not selling these..if a sponser is interested they could become available..

Wow nice work!
How much do you have in one of those?

Pretty Darn Cool!!!

Can you give me any more info on how it works? What do you do for a living?

luvsaws said:

Wow nice work!
How much do you have in one of those?

Click to expand...

So far $10 in parts not counting the PCB board,but that stuff is cheap..my friend has the CAD operated machine to cut the boards.

" JoshRountree Pretty Darn Cool!!!

Can you give me any more info on how it works? What do you do for a living? "

what do i do for a living ?? as little as possible ! LOL !

how it works,, the chip has a built in oscillator and when used with the external crystal a comparison is made between the code set in the chip and the input signal and the RPM is derived from that..
the chip runs off 5 volts and the board has a regulator on it so any battery more than 5 volts will work to power it..
the LED driver is the glitch now,,as it is a 9 volt bad prob wont last more that a year if used daily..

my friend is a nut on accuracy,,thinks 10 rpm at 20k rpm not good enuf !!

told him we need input from the saw guys for this one..
he upset because the 11th digit on his counter fluctuates ! LOL !

That's a very cool project you have going there. Your accuracy is more than enough. How does it get it's input signal? Is it wireless?

Wow, Ron that's pretty cool. I want one...

That's seriously cool!!! Nice project and I think there will be a lot of interest!!

10 RPM, that's plenty accurate enough for what we do.

So how does it read over 10k with only 4 digits?

Roncoinc, it won't let me rep you! This is the sort of project I LIVE for! You rock!

(Everybody else: These guys are your daddies, whether you know it or not)

EDIT: further research suggests that an Arduino controller might make a great 555 timer-based platform for something with great precision for cheap and easy.

Very cool Ron.

Silicon Chip and Jaycar here do an LCD readout tacho as a kit but IIRC it only goes to 9999RPM.
I always assumed the problem was the four digit readout and a five digit one would 'fix' it, obviously not, so i'm assuming it's the counter ?

I'm just trying to dig out my catalogue and check so you have something as a reference/ideas.

I like it!!
Hurry up and start shipping 'em out!!

If it ain't got nuts and bolts, and can't be welded I'm lost on the details,but it sounds good so far!


Stay safe!
Dingeryote

Nice work!

So how do you have your chipset connected? Does the pcb actually have inner traces or just using external jumper wires? +1 on using SMT parts, thru hole is outdated and takes up too large a footprint. We've pretty much done away with thru hole electrolytic caps in favor of surface mount and compliant (interference fit) pin mount to do away with wave soldering.

That board definately brings back a lot of memories, thanks for sharing!

Very cool!

Very Cool Indeed!!!

I/we will be awaiting further developments!! This sounds like the "perfect" DIY project for us (cheap) saw nuts!!! If this could be had/made for $10-$20 I for one would not worry about springing for a 9V battery once a yr!! Please continue!!!!! (read that as BIG interest!!)

Neat. That looks like a million dollar solution to a $ 80 problem.

Great idea!

I was looking this morning for a tach for tuning my saws...

more info

A little history on this project and how it came about...
needing a cheap easy solution to reading "IF" frequency in "RF" transmiters we made up board..that soon developed into one that would read the IF and by a switch the frequency after it was mixed and on the way to it's final output.one of the first changes was to have the decimal point movable by a switch,say the readout gave in the range of 37mhz,move the point to eliminate the 37 and have two more digits of resolution..on a four digit board it worked fine..the transistion to include a 5 digit readout took a lot more parts,not as simple as just adding another digit and added to the cost and size of the board.. also found that the code for stabalizing the last digit without losing accuracy was a pita.multiplexing the displays helped but could cause it's own noise at certain ranges..

Now being as cheap as i am i could not see the prices asked for tachs as being resonable for what they are..so we decided to build a beta board for a single cyl two stroke.
i didnt want to breadboard and my friend has the PCB cutter so he started on it yestday afternoon..
i started stripping down the code in the .hex file i have from the original board but he decided to write the code from new as it would be quicker than to wait for me.
a couple hours later he had the pcb designed and cut and did the code while the machine was cutting the board.
he tested it out and was surprised how nice it works..
am going to ask him to cut a couple extra boards to send and the parts..
now MY work begins,testing and making sure his code is clean,putting to a saw and working any bugs out.. should be FUN !!
hope to be able to eliminate the crystal and variable resistor used to adjust output and use the referance occilator in the chip.
a picture of the board with some parts marked to get a better idea of it..

answers

" That's a very cool project you have going there. Your accuracy is more than enough. How does it get it's input signal? Is it wireless? "

going to try it both ways..have to find out how sensative it is first.

" 10 RPM, that's plenty accurate enough for what we do.

So how does it read over 10k with only 4 digits? "

Take 15,500 rpm,drop the first digit and only use the last four..if your saws runs under 1,000rpm your out of luck
if your into the 20k range you got a HOT saw !

" EDIT: further research suggests that an Arduino controller might make a great 555 timer-based platform for something with great precision for cheap and easy. "

555's are nice little ic's but a "PIC" has it all built in a a MC is needed anyway.

" So how do you have your chipset connected? Does the pcb actually have inner traces or just using external jumper wires? +1 on using SMT parts, thru hole is outdated and takes up too large a footprint. We've pretty much done away with thru hole electrolytic caps in favor of surface mount and compliant (interference fit) pin mount to do away with wave soldering.

That board definately brings back a lot of memories, thanks for sharing! "

The board is machine cut single sided PCB..
thinking if sometime in the future "IF" it is made available as a kit,thruhole will be used so the end user can assemble.
not worried about the footprint,look at the size of it now and after trimming the board ? even smaller and will be made even smaller if and when they are put out.

these are NOT for sale, i am not a sponsor,i cant sell here..
i am just looking for input and suggestions for the development of this project from people that would use it.
eventually i would like to send a couple of kits out to have end users evaluate it and then maybe a sponser would be interested in distribution.
Now the guy i work with on these things is,uh,well,easily distracted i should say and sometimes projects take a bit of time..i was surprised he knocked this one out within hours of discussing it.
as progress is made and it develops i will post if there is enough interest.
tnx for any input..

cool beans. gonna have to toss my paperclip/rubberband idea

Ron, here's a pic of the Jaycar/Silicon Chip kit for reference





It only goes to 9900RPM, and for magneto use they recommend

You could try connecting the red wire from the magneto to the "ignition coil -ve" input on the tachometer. If this doesn't work try the yellow trigger wire at the "low input" on the tachometer instead.

Note that the 2.2μF capacitor at the anode of D1 may need to be removed from circuit for successful operation.

{edit}Forgot to add that it was designed primarily for car use, I only added it to the thread as it's a tacho kit that you assemble at home.