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Homemade tachometer build

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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.

 

shhhhhh!

 

I'm surprised no one has asked for Bluetooth to an IPhone app yet.

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shhhhhh!

 

I'm surprised no one has asked for Bluetooth to an IPhone app yet.

 

can we have an android app for it Chuck? :ychain:

looks good, maybe i should put my brother to work :eusa-think:

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I have a few 555 timers sitting in my droor that I use for some relay projects with trains. I think I might give this a go, cheap and a fun easy project. I can read a schematic, understand the functions of components but I lack the part of coming of with these circuits. I need to do some more studying of the 555 timer data sheet to learn a bit more. On the plus side , I can repair lots of electronics because I understand the functions of things  but I really admire the way some guys put it all together from scratch. ( compliment to you ) I need to hone that part of the skill.

 

I wonder if the few radio shacks around would have a simple meter like you have used or if I have to order some through an electronic supply house? Also, How responsive is this setup? I believe it would respond fairly quick due to the layout you have going. Great job.

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A good photo of both sides of the board Would be a tremendous help.

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I think you would find trying to compare the back to the front confusing. The schematic would be what to follow and come up with a clean arrangement. Sometimes it gets confusing just flipping the board around and soldering components. However, I am sure SOI has a clean arrangement already and it could help from that perspective. Since SOI has limited time, I would be happy to help anyone read the schematic if they have some trouble with it. Its all simple components and symbols.

Edited by Theroundhousernr

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The schematic is essential. A photo will go a long way for some less experienced to get an idea as to where to place the parts and the cleanest way to put everything together.

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This may help Nick. A pic of the underside of the board, warts and all. Several solder tips need to be removed, some retouched, and a good dose of IPA to clean off the flux residue.

 

The construction is on "stripboard". Each horizontal copper strip can be considered a wire. Any component needing to be connected together can be joined to that "wire".

 

If any wires need to be broken (areas highlighted in green) as in the case of under the 555 timer chip, the copper trace can be peeled away with an exacto knife or removed with a drill bit in "spot cutter" fashion. Copper traces can be joined together with jumpers (outlined in pink).

 

 

post-1689-0-13111000-1426564753_thumb.jp

post-1689-0-79195300-1426569014_thumb.jp

post-1689-0-26730400-1426589751_thumb.jp

Edited by Save Old Iron
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I wonder if the few radio shacks around would have a simple meter like you have used or if I have to order some through an electronic supply house? Also, How responsive is this setup? I believe it would respond fairly quick due to the layout you have going. Great job.

 

Remember, I used a Simpson 260 meter on the 50uA current scale for the initial testing. The readout meter can be any analog meter with a 50uA current scale.

 

The other option is to build the circuit, place it in a small case with leads that plug into an analog meter. Set your meter to the 50uA scale and read the RPM off the handheld meter.

 

This is an inexpensive analog (~15$ off eBay) using the 50uA current range and reading off the 0 - 50 scale.

post-1689-0-14819400-1426570833_thumb.jp

Edited by Save Old Iron
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Also, How responsive is this setup? .

 

This depends on a few factors. The most significant factor is the mechanical "liveliness" of the meter movement itself. Some meters are quick to respond and overshoot their target (under-dampened) and some are sluggish and slowly crawl up to their final position (over-dampened). And some hit the Goldilock's spot - just right.

 

If you have a slow. over-dampened meter, there is not much that can be done electronically to liven it up.

 

A lively meter movement can be tamed by placing a capacitor across its input terminals. This will slow down the meter movement somewhat but still provide an accurate reading when the pointer does come to rest.. This is the method I have chosen in the schematic above. The 100ufd capacitor across the meter movement removes any jumpiness of the meter movement at very slow RPM's. This particular circuit can read down to the 500 - 600 RPM range without becoming too jumpy or having the meter movement "pump".. This feature is very helpful to confirm good cranking speeds with reasonable accuracy. Remember, at 500 RPM on a 1 cylinder engine, the points are only opening and closing less than 5 times per second. Take your finger and wag it 5 times per second - back and forth. This is what an analog meter pointer would do if it were not for the 100 ufd capacitor across the meter leads.

Edited by Save Old Iron
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Yes, I saw the cap parallel with the meter. Thanks for the explanation. Now the only issue for me is I have no way of generating accurate constant pulse to calibrate. Might have to borrow a tach.

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I wonder if the few radio shacks around would have .

 

The demise of Radio Shack has taken away some of the breadboard options I presented in the opening posts of this thread. I'm not sure if the prototype pcb's they offered will remain available, therefore I switched gears to construct the circuit on stripboard.

 

This is a robust circuit that will work well with any style of prototype board construction.

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Yes, I saw the cap parallel with the meter. Thanks for the explanation. Now the only issue for me is I have no way of generating accurate constant pulse to calibrate. Might have to borrow a tach.

 

 

Wire up a small 12 volt transformer with a "clipper circuit" on the secondary windings. If you construct a simple 5 volt power supply off the same secondary windings, you can power a flip flop to cut the 60 Hz line frequency into 30Hz - perfect for an accurate 3600 RPM cal standard. A second flip flop in series would yield 15Hz to use as a check for 1800 RPM idle speed on the engine.

 

Be extremely cautious building and working with any device connected directly to the 120 VAC mains in your home.

Edited by Save Old Iron
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Ah prefect. So rectify the current and then maybe a lm7805 regulator but don't smooth off the current. Using half wave dc?

or

 

check your multimeter. If it has a FREQ or HZ function, you can slap together an astable 555 timer to output a pulse stream. Adjust the 555 circuit to read 30.0 Hz on your multimeter and you can avoid a mains powered calibrator.

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Done and done. A 30 Hz calibrator from nearly the same components needed to build the tach circuit.

 

If need be, I can mail this out to you, you can calibrate your tach (or compare this to your own tach calibrator) and then you can forward it on to the next person to use.

post-1689-0-50769100-1426733585_thumb.jp

post-1689-0-33396700-1426735702_thumb.jp

post-1689-0-30497000-1426748209_thumb.pn

Edited by Save Old Iron
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I'm trying to adapt this circuit to a motorcycle without Breaker points. If I'm reading this diagram correctly, I can just attach the input to the negative side of the coil? What about using an inductive pickup (i.e. wrapping a few turns of wire around the spark plug wire)? BTW, my bike is 1 cyl and fires the plug every crank revolution so I'll be using a 100ua meter and modifying the face. 100 ua will equal 5000 rpms, 50 ua will be 2500 rpms, etc. Sorry for the off topic question. Maybe someone can help.

555 tach 1cy 4 stroke rev2.gif

 

 

 

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Unfortunately  electronics is a subject not many of us are well versed on. There are a "couple" experts out there hopefully they will chime in. Others may be hibernating . Squirrels do that.:teasing-poke:

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It's not really my field of expertise either. I know enough to get myself in trouble! I'm glad I found this thread though. It's given me a few ideas.

 

Since it is Winter, I'll be patient and wait for the squirrels to wake up! :D

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