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Post by ernie wrenn on Aug 31, 2011 20:09:47 GMT -5
rythmnbls
Beautiful job on your turbine... Now How can I make a digital tach for my J34-34? It has the standard impulse tach generator @4200=100%, but I am logic stupid..
Being 62 I still fix vacumn tube equipment. I would like a LARGE readout because of the distance I must mount it, approx 3 feet. Color needs to be bright and easy to see, red blue etc. Any ideas?
ernie
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Post by propellanttech on Aug 31, 2011 20:13:26 GMT -5
rythmnbls Beautiful job on your turbine... Now How can I make a digital tach for my J34-34? It has the standard impulse tach generator @4200=100%, but I am logic stupid.. Being 62 I still fix vacumn tube equipment. I would like a LARGE readout because of the distance I must mount it, approx 3 feet. Color needs to be bright and easy to see, red blue etc. Any ideas? ernie Where are you located....and how much do you want to spend? Ok correction.....I see where you are located......how much you want to spend?James |
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wolfdragon
Senior Member
Joined: April 2011
Posts: 287
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Post by wolfdragon on Aug 31, 2011 20:32:16 GMT -5
ernie, I am making one that can output to a digital or analog tach of any make/brand
basically it will be the optical pickup with a freq divider after it to make it act like a 4, 6, or 8 cylinder distributor cap
if you want a quick and dirty schematic I can put one together, i can even use the output of the omron box everyone seems to love on the yahoo group to make the pickup easier
of course you will have to add a zero or two depending on the range of the tach and the actual RPM, but at least it gets things back to off the shelf gauges
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Post by ernie wrenn on Sept 1, 2011 9:21:49 GMT -5
Cost is not a major concern, with in reason. I like the idea of off the shelf. What Omron box are they using?
These military tack"s suck>
ernie
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Post by propellanttech on Sept 1, 2011 9:41:25 GMT -5
I figure we are talking about digital readout tachs, and not needle tachs.
Would be pretty easy to make a pulse divider circuit to do this.
James
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Post by turbochris on Sept 1, 2011 9:57:18 GMT -5
Most existing tach generators are 3 phase generators and they usually run at 4200 rpm at 100% So, at 100% I have 70Hz, could I filter one of the phases and use that to run a digital tach? I'm with Ernie, I'm getting old and a big display helps.
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Post by propellanttech on Sept 1, 2011 10:10:04 GMT -5
Most existing tach generators are 3 phase generators and they usually run at 4200 rpm at 100% So, at 100% I have 70Hz, could I filter one of the phases and use that to run a digital tach? I'm with Ernie, I'm getting old and a big display helps. Well you could, but you would need to insure a few things. First your readings would be somewhat hard to read. 4200 rpm =100% You would need to extrapolate from there. Also, you would need to insure the output voltage didn't exceed the rate voltage of the tachometer. You could use a clamping diode with a resistor to insure the rated voltage was never exceeded. You would also want to insure the voltage only goes one way (pulsed DC instead of AC). This would just require a diode on the tach input line rated for the input voltage. It should work....although that may sound like a lot. James |
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wolfdragon
Senior Member
Joined: April 2011
Posts: 287
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Post by wolfdragon on Sept 2, 2011 8:33:36 GMT -5
ernie, can you get us more info on what the waveform looks like?
You will probably need to use an oscilloscope to get the full picture... but
If it is three phase, is it on one wire or three? Can you set a multimeter to peak and rms voltage modes to get the peak and rms of the AC output (if it is AC...)
The more that is known about the source signal the better. That will drive whether or not the signal requires rectifiying to DC, filtering out specific noise domains, knocking down to a voltage level, dividing/multiplying the freq, etc...
All of that just to match whatever digital display or tachometer you want to see the RPM on.
Too bad I don't live near GA anymore, I'd bring my scope down and help you in person.
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Post by ernie wrenn on Sept 2, 2011 8:44:16 GMT -5
Chris
HELP!! I think he said a dirty word.... Can you do this with a tach drive in a lathe? It is a standard 3 pin generator coming off the acc drive.
I would love a 3 inch high display with 5 digits. My max RPM is 14,500.
ernie
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Post by propellanttech on Sept 2, 2011 12:24:26 GMT -5
Chris HELP!! I think he said a dirty word.... Can you do this with a tach drive in a lathe? It is a standard 3 pin generator coming off the acc drive. I would love a 3 inch high display with 5 digits. My max RPM is 14,500. ernie Ernie, Because it is only 3 pins, you probably have three phase AC coming out, but Wolf is right. Getting the waveform would be the best option to insure you do not "toast" something. James |
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rythmnbls
Veteran Member
Joined: August 2011
Posts: 145
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Post by rythmnbls on Sept 3, 2011 13:52:40 GMT -5
Ernie, My tach was built from an arduino uno and a 20x4 character LCD with white on blue pixels. You can get an idea on how to wire one up here.The display isn't that big so reading it at 3' away would be tough, although programming it to to use a large custom font has been done before, an example here. If you're interested in more details, let me know and I'll post it here. Regards, Steve. |
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Post by propellanttech on Sept 3, 2011 13:58:54 GMT -5
Ernie, My tach was built from an arduino uno and a 20x4 character LCD with white on blue pixels. You can get an idea on how to wire one up here.The display isn't that big so reading it at 3' away would be tough, although programming it to to use a large custom font has been done before, an example here. If you're interested in more details, let me know and I'll post it here. Regards, Steve. I would like to know more about the monitoring part of the system. The Tachometer and readout are the easy part for me. Also.....You could have a remotely mounted display....that way it wouldn't need to be so big. The communication should run 5-10 feet. James |
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Post by turbochris on Sept 4, 2011 15:28:40 GMT -5
It's a 3 phase generator driving a 3 phase motor inside the tach itself. I have a place to tap in with a meter, i checked the waveform once but I was looking for 70 hz and didn't look at the peak V or pay much attention to the shape of the wave. I could check it next time I start it up. They're all pretty much 3 wire 3 phase but some use ground as the 3rd wire and only have 2 contacts on the connector.
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wolfdragon
Senior Member
Joined: April 2011
Posts: 287
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Post by wolfdragon on Sept 4, 2011 16:51:43 GMT -5
Chris when you get the chance:
Vpeak and the freq are the most important, especially how the freq varies with actual RPM
if you can scope it, it would be nice to know how the wave looks (makes it easier to chop if you know how wide the chop will be past a given voltage)
If it is outputting what I think it would be outputting (because it the most straightforward way for that setup you describe to work) it should be as simple as knocking into DC at a lower voltage, use a comparator to put it into a square wave, and set the output square wave voltage to something useful
maybe a little bit in the freq changing dept, but depending on what device you are driving, that will really influence what the circuit puts out since it needs to match up to the intended display device
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Post by turbochris on Sept 5, 2011 7:24:36 GMT -5
Ernie has a few loose tach generators. I guess I'll go visit him with my scope and we'll spool some up in the drill press.
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