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posifour11

Homemade tachometer build

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Hey Old,

Been interested in this project. I ordered the meter. Will continue to follow. You do great work.

Marvin

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Chuck, my meter is on its way from Chinaland. I can swing through "the big city" on Sunday on my way home from drill.

Edited by posifour11

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Thanks for the patience guys. I have been trying to find the "best" parts for circuit performance but Radio Shack carries so little anymore in the stores. The "right" parts may only be able to be ordered on line. I'm also trying to work with the issue of not having to use a $3 "in store" part when a $1 part can be ordered online.

 

Let's at least get the circuit board and major in store parts list created. Hopefully I'll be able get to the list in the next day or so. You should be able to grab many of the parts and start construction in a day or two.

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Here is the circuit we will be working with. I'm working on a parts list as I speak. Hopefully all following this will be able to obtain most of these items at Radio Shack.

 

Stay tuned for a circuit explanation and a parts list.

post-1689-0-07082700-1373789597_thumb.gi

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Functional areas of the circuit are outlined in color.

 

Components in the orange area are located on the tractor. The ignition points and primary of the ignition coil are shown.

 

Components in the green area are used to shape the ignition points electrical signal and limit the voltage level to allow proper triggering of the tachometer electronics.

 

Components in the purple area provide a stable voltage to the tach circuit by accepting battery voltage from 10 volts to above 16 volts and outputting a constant voltage near 7.5 to 8 volts to the tach circuit. This stable voltage will keep the tach reading from varying if the battery voltage varies.

 

Components in the pink area display the RPM's on an analog meter and allow for calibration of the meter reading to show the correct RPM on the meter.

post-1689-0-32496200-1373791846_thumb.gi

Edited by Save Old Iron

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this is the best I could do with "in store" available parts from Radio Shack

 

555 timer.......................(1)pn 276-1718
breadboard...................(1)pn 276-170
adj volt regulator...........(1)pn 276-1778
4.7k resistors................1pk of 5
1k resistors...................1pk of 5 pn 271-1118
47k resistors.................1pk of 5 pn 271-1130
.01uf cap.......................(1)
.1 uf cap........................(3)
10 uf cap.......................(1)
hookup wire
220 uf cap.....................(1)
100k pot........................(1)pn 271-284
100k resistor.................1pk of 5  pn 271-1131
(or 200k pot)
5 volt zener diode..........(1)pn 276-565
8 pin retention socket....(1)pn 276-1995

 

 

You will have to decide on how you wish to proceed. Visiting the Radio Shack store will get you most BUT NOT ALL the parts you will need. Ordering from them online - or from another parts supplier such as Jameco.com will get you the RIGHT PARTS THE FIRST TIME. What you spend in shipping for an order you will save in gas and most likely frustration on not having all the parts you need at one time.

 

Check out the Jameco website and decide if they have appropriate shipping charges to your area.

 

http://www.jameco.com/webapp/wcs/stores/servlet/StoreCatalogDisplay?langId=-1&storeId=10001&catalogId=10001

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Consider this homework for now - until I can post later tonight

 

 

 

post-1689-0-61187500-1373795911_thumb.gi

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Amazing as usual. If I'm getting one thing online, may as well get everything online to save time and frustration.

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my meter has arrived.

Marvin

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I have not forgotten about you guys. Work has been insane and I just got off 22 days straight without a day off. I'll be posting more in the next few days.

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Not yet. I've been too busy to think and, I gather, Chuck has as well hope to slow down soon and get to building.

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Wow. That time flew by fast. My apologies but things have been off the wall at work. I have a few weeks vacation coming up this month and I promise I will spend some time on this putting together a buy list.

 

Radio Shack will not have all the parts needed and will generally be more costly then going to a reputable parts supplier for the hobbyist like JAMECO.

 

Once we get the build list complete, we can start with the actual build of the circuit board. I plan to supply enough detail on the build to hopefully allow anyone else who may be interested to follow along and construct a useable piece of test gear.

 

555tachbreadboardtheory_zpsa48ae1f9.gif

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This is very interesting, I had been trying to think how I could use an inexpensive car tachometer but could not find one for a single cylinder engine. They are generally switchable between 4, 6 & 8 cylinder modes so would need a circuit to reduce the number of electrical pulses to correspond to a 4, 6 or 8 cylinder engine.

Your circuit seems much easier, did yet get finished and do you have a circuit diagram marked up with the component values? I'm sure I can translate the circuit on to some strip board and soldering up a circuit is no problem.

Andrew

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What happened to the rest of the project?????

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We did wander off into the weeds on this one.

 

The circuitry was taken from the breadboard stage to the final? functional perfboard stage

 

 

555%20tach%20008rs_zpsmuuw4tjx.jpg

 

 

Circuit layout is not critical for this project to perform properly, any buildup on perfboard will work fine.

 

 

555%20tach%20016rs_zpsxgt06u2j.jpg

 

 

On a single cylinder Kohler, the points are opening and closing at a rate of 15 times per second (or 15 Hz)

 

 

555%20tach%2015hz%20rs_zpsccratufn.jpg

 

 

Simulating this frequency on a pulse generator results in a correct display of 1800 RPM.

 

 

555%20tach%201800%20rs_zps1md3gmkk.jpg

 

 

Increasing the frequency to 30 Hz, as would be seen on a single cylinder engine running at 3600 RPM, the display shows excellent linearity.

 

 

555%20tach%2030hz%20rs_zpsuxoo7lff.jpg

 

 

555%20tach%203600%20rs_zpsrs0motf6.jpg

 

 

The circuit is stable over a range of 6.3 volts to 35 volts and draws less than 0.010 amps.

The circuit can be powered by a 9 volt battery with over 40 hours cumulative use from a single battery. Since the circuit will only be powered for minutes at a time, battery life in normal use will be over a year.

 

The circuit can also be powered off the tractor battery if needed. A 5 volt internal voltage regulator is mounted on the circuit to provide stable and repeatable RPM indications over a wide range of power conditions.

Edited by Save Old Iron

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Conceptually, my intent is to gut an inexpensive handheld analog multimeter and install a custom fit perfboard inside a handheld case.

 

 

555%20tach%20pc%20in%20case_zpsxvrlpsy4.

 

 

After building and using the analog tach, I forgot just how much I would rather deal with a smooth operating pointer rather than jumping digits!

 

I'm sure you folks will have a few questions. I only get on RS a few days a month, so please be patient if an answer is not immediate.

Edited by Save Old Iron

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I have also had a request to recalibrate the 3 cylinder setting of a Heathkit ID-29 to read 1 cylinder 4 cycle signals.

 

I'll be giving that a go later this summer.

 

 

heathkit%20id29_zpssy90klx8.jpg

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Most recent schematic w/ updated values for filter capacitors

 

 

 

post-1689-0-73080200-1426333047_thumb.gi

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So could this be adapted to a magnum twin or command twin with magnetic coils/ no points? I have most of the parts except the digital readout. I wish I could write code so I could try to make something out of these Ti launchpad boards I have. Just cant seem to pick it up. Thanks for all the info so far.

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So could this be adapted to a magnum twin or command twin with magnetic coils/ no points? .

 

Sure can. Modifying the values / configuration of the trigger circuitry [R1 C1 D1] will allow triggering off one plug wire. Setup would be similar to a "tiny tach" w/ loops of wire around the sparkplug wire as the input signal.

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Hmmmm  .....with a little modification and a small telescopic antenna in the handheld case, we could most likely go wireless with this circuit.

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great work Chuck - with a simple mod you can make it run from the stator.

 

That will give you 18 pulses per second and smooth things out - it also makes it agnostic to the number of cylinders.

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