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Any electronic engineers amongst us?

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warren3200gt
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Any electronic engineers amongst us?

#1 PostAuthor: warren3200gt » Fri Nov 24, 2017 2:58 pm

As winters here I wanted a small project that can be done in comfort of a warm dining room! I want to make a led bar graph rpm counter so went looking for a circuit diagram which would do the required.
Below is the clearest simplest I could find but has way more led's than I want to use. Just want to have 6 green, 2 yellow, one red, giving 9k rpm in total. I have a load of these leds that I was going to use set into an arced housing around a centralised speedo
So......
Can anyone alter the diagram below or has a diagram that will do what I want :?:
Diagram deleted so as not to confuse
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Last edited by warren3200gt on Wed Dec 06, 2017 9:31 am, edited 1 time in total.
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Re: Any electronic engineers amongst us?

#2 PostAuthor: ZedHead » Fri Nov 24, 2017 3:42 pm

The LM2917 is a frequency to voltage ic in this diagram feeding 2 led bargraph drivers. It is fairly easy to chop this down to one LM3914 driving 9 leds.

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Re: Any electronic engineers amongst us?

#3 PostAuthor: warren3200gt » Fri Nov 24, 2017 3:54 pm

Being an electronic numpty, how? I can build from a diagram but know sweet FA about what's actually going on in the circuit. Then its fingers crossed if it works. If it didn't I wouldn't know why or how to fix it! :oops:
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Re: Any electronic engineers amongst us?

#4 PostAuthor: Gus » Fri Nov 24, 2017 3:59 pm

Having watched his video can you not just connect your leds to the outputs that you want (relative to rpm) and leave the others empty. As his circuit leaves the previous leds lit I'm assuming this will stay the same until the circuit passes over the empty output(s) until it gets to the next led.

Nip down to Maplins with the parts list.

Or send him the question.

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Re: Any electronic engineers amongst us?

#5 PostAuthor: warren3200gt » Fri Nov 24, 2017 4:09 pm

I don't know if that would work Gus. I don't know if the driver needs something (LED?) on every outlet to work or if you skip one the next in the sequence will work?
I was hoping someone could tell me or re draw that diagram to just one driver as Zedhead suggests. The LM2917 bit is the bit I don't understand. Would it work if I just not do the C4, R2, DZ1 C6,C7, and R5 wires? leaving terminal 2 & 3 on the LM2917 empty? which would isolate it to one driver.
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Re: Any electronic engineers amongst us?

#6 PostAuthor: Gus » Fri Nov 24, 2017 4:28 pm

Or could you put a resistor equivalent to the led in place of the led?

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Re: Any electronic engineers amongst us?

#7 PostAuthor: warren3200gt » Fri Nov 24, 2017 4:33 pm

That would work I guess but there's no point in over complicating it unless I have to. If I new how to cut it back to one driver it would be simpler and less chance of cocking it up.
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Re: Any electronic engineers amongst us?

#8 PostAuthor: ZedHead » Fri Nov 24, 2017 6:09 pm

warren3200gt wrote:I don't know if that would work Gus. I don't know if the driver needs something (LED?) on every outlet to work or if you skip one the next in the sequence will work?
I was hoping someone could tell me or re draw that diagram to just one driver as Zedhead suggests. The LM2917 bit is the bit I don't understand. Would it work if I just not do the C4, R2, DZ1 C6,C7, and R5 wires? leaving terminal 2 & 3 on the LM2917 empty? which would isolate it to one driver.


A bit more complicated than that. let me have a think

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Re: Any electronic engineers amongst us?

#9 PostAuthor: garyd » Fri Nov 24, 2017 6:25 pm

just connect your leds to the outputs that you want (relative to rpm) and leave the others empty.

This will work fine...but if your concerned just measure the resitsance of the LED and put a resistor in it's place.

But I'm sure the Pins on the IC don't need to be connedcted to anything as the IC has no way of knowing if it's connected or not (i.e. there's no feedback to the IC for it to check.

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Re: Any electronic engineers amongst us?

#10 PostAuthor: ZedHead » Fri Nov 24, 2017 7:08 pm

Leaving out the LED's is not the problem.

The circuit is designed to light all 20 leds at maximum revs. Even though it allows for some adjustment the danger is it will peak out well before the desired 9k.

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Re: Any electronic engineers amongst us?

#11 PostAuthor: warren3200gt » Fri Nov 24, 2017 8:01 pm

Ok thanks for that, So bearing in mind wasted spark it should read one pulse per one rev. Ie it wont read twice or half the desired amount?
So from a syncing revs to leds, the only way to do it would be add the leds when the revs are at the desired amount. Ie with the engine running at 1k add the led to the last outlet that illuminates it. Then again at 2k etc, etc?
What I was hoping to achieve was 1 led at 1k, 2 at 2k, 3 at 3k etc. Or is there way of adding in a variable that i could adjust to achieve the desired effect?
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Re: Any electronic engineers amongst us?

#12 PostAuthor: garyd » Sat Nov 25, 2017 7:43 am

Not really sure what your saying.

Do you want more LEDs lit for more RPM ( lick 6 LEDs for 6K ) or do you want just one LED lit showing current RPM?

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Re: Any electronic engineers amongst us?

#13 PostAuthor: garyd » Sat Nov 25, 2017 7:44 am

garyd wrote:Not really sure what your saying.

Do you want more LEDs lit for more RPM ( i.e. 6 LEDs for 6K ) or do you want just one LED lit showing current RPM?

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Re: Any electronic engineers amongst us?

#14 PostAuthor: warren3200gt » Sat Nov 25, 2017 8:38 am

Gary, what I'm trying to achieve is an arc of 9 leds. At 1k rpm 1 led is lit, at 2k rpm 2 are lit, at 3k rpm 3 are lit etc. The only way of doing that using the circuit below would be to build it, stick it on the bike, run the bike at 1k and test which driver outputs give current, again at 2k rpm and test, again at 3k rpm and test. Then add leds to the relevant driver out puts. I was wondering if I could add in a control mechanism so that I could use one driver, add leds to all the outputs, start the engine and "turn the knob" on the control mechanism to sync the lit leds to the engine rpm.? Some sort of variable resistor or something and where to put it in the circuit?
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Re: Any electronic engineers amongst us?

#15 PostAuthor: Gus » Sat Nov 25, 2017 11:05 am

you could wire all the leds, rev the bike and mark which leds are lit when you want, disconnect the rest.

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