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Any electronic engineers amongst us?

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warren3200gt
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Re: Any electronic engineers amongst us?

#46 PostAuthor: warren3200gt » Tue Dec 19, 2017 8:38 am

Ok, all the bits are here. One of my customers believes that the trimmer pot currently at 150k will be far too sensitive due to the large range it covers and ideally needs to be 4.7k. Does that sound about right? Anyway I have grabbed a 5k one from Maplins so now I have all the bits and can easily swop pots after a trial if needed. just need some time to check it all out now. As usual Christmas gets in the way of everything fun :D
PUM 488 June 2023
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Re: Any electronic engineers amongst us?

#47 PostAuthor: ZedHead » Tue Dec 19, 2017 9:04 am

Warren, the values of C6 and R5 determine the signal voltage going to pin 5 of the led driver ic and have been chosen to give about 5 volts @ 9k revs with the trimmer near the middle. If you use a 5k trimmer you will need to put a fixed resister at the ground end. Something like 68k - 82k should give you something to work with.

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Re: Any electronic engineers amongst us?

#48 PostAuthor: warren3200gt » Tue Dec 19, 2017 9:12 am

I'll try with the 150k one first and see just how sensitive it is.
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Re: Any electronic engineers amongst us?

#49 PostAuthor: DogsbolloxofZ1B » Sat Dec 23, 2017 10:01 pm

get yourself a mini brick plc interface firing cc’t as rpm input and
generate small amount of plc code to drive LED
vis digi outputs based on freq of firing cc’t.

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Re: Any electronic engineers amongst us?

#50 PostAuthor: warren3200gt » Sat Dec 23, 2017 10:45 pm

Wot u talking bout Willis?
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Re: Any electronic engineers amongst us?

#51 PostAuthor: warren3200gt » Sun Dec 24, 2017 1:20 pm

Hhhmmmmm, that didn't do what I expected!
Built the circuit on a breadboard. Resistor are non directional, capacitors are non directional, diodes ARE dirctional. Checked and double checked it. Not sure if it would make a difference but only first 3 leds were attached?
With ignition on without engine running.
With the trimmer on zero all the leds were lit. Trimmer on full all the leds are lit.
With engine running on tick over.
With the trimmer on zero all the leds were lit. Trimmer on full all the leds are lit.
Help!!!!!!!!!
PUM 488 June 2023
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Re: Any electronic engineers amongst us?

#52 PostAuthor: ZedHead » Sun Dec 24, 2017 6:44 pm

Measure the voltages at pin 5 to ground of the LM3914 at different revs and trim settings. Also pin 6&7 which should be a fixed voltage

Next disconnected pin 5 of the LM3914 and confirm all LED's go out out. If they stay on the LM3914 is wired wrong.

C2 is electrolytic and polarised.

If you you get stuck you can post the breadboard to me and I will check it

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warren3200gt
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Re: Any electronic engineers amongst us?

#53 PostAuthor: warren3200gt » Sun Dec 24, 2017 6:53 pm

Thanks I'll check those tomorrow.
Ìf C2 is back to front would that cause it or would it not work at all?
Also not sure if you noticed but i amended my post re the number of leds attached. Does it need all 9 attached or will first 3 do for testing?
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Re: Any electronic engineers amongst us?

#54 PostAuthor: warren3200gt » Mon Dec 25, 2017 3:10 pm

Ok seem to have cocked up lm3914 connections. Feed 5 at about 1500 rpm is 3.4v and increases as revs do. Removed feed to lm3914 pin 5 and leds remained lit.
Going festive for a week now due er indoors so I'll update on sorting it next week.
PUM 488 June 2023
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Re: Any electronic engineers amongst us?

#55 PostAuthor: warren3200gt » Mon Dec 25, 2017 11:38 pm

D1 live switched wire. Is that a 4 way junction ? or should D1 to pin 9 jump c2/c3 to leds? Like this.
Diagram deleted as it didn't work.
PUM 488 June 2023
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Re: Any electronic engineers amongst us?

#56 PostAuthor: warren3200gt » Wed Jan 03, 2018 2:21 pm

Yeah, almost there. With it wired up like the diagram below I have partial success but something needs tweaking.
If I adjust R5 so that LED no 1 is just on at 1k rpm as read by a digital tacho reading off the HT lead, led 2 comes on about 1700rpm, led 3 comes on at 2500 rpm.
diagram deleted to not cause confusion.
Last edited by warren3200gt on Thu Jan 04, 2018 2:04 pm, edited 2 times in total.
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Re: Any electronic engineers amongst us?

#57 PostAuthor: garyd » Wed Jan 03, 2018 5:43 pm

Looking at lm3914., It's R6 & R7 that might need the adjustment

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Re: Any electronic engineers amongst us?

#58 PostAuthor: warren3200gt » Wed Jan 03, 2018 5:57 pm

Hi Gary, as you may have noticed I've no idea what makes electronics work but am happy to play with them. Luckily this is only 12v at most so not likely to kill me :D
Do you or anyone know or could you or anyone calculate what they need changing to?
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Re: Any electronic engineers amongst us?

#59 PostAuthor: garyd » Wed Jan 03, 2018 8:04 pm

Ah....now looking at the proper specs for that chip....That controls the brightness of the LEDs :oops:

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Re: Any electronic engineers amongst us?

#60 PostAuthor: garyd » Wed Jan 03, 2018 8:23 pm

Copied from texas instruments....(the example is the same as you are using)

LM3914
www.ti.com
SNVS761B
– JANUARY 2000
– REVISED MARCH2013
FUNCTIONAL DESCRIPTION
The simplified LM3914 Block diagram Is to Give the General idea Of the circuit's operation.
A High input Impedance buffer operates with signals from ground to 12V, and is protected against reverse and overvoltage signals. The signal Is then applied to a series of 10 comparators; each of which is biased to a different comparison level
by the resistor string.

In the example illustrated, the resistor string is connected to the internal 1.25V reference voltage. In this case, for each 125mV that the input signal increases, a comparator will switch on another indicating LED. This Resistor divider can be
connected between any 2 voltages, providing that hhey are 1.5V below V +
And no Less than V − . If an expanded scale Meter display is desired, the total divider voltage can be as little as 200mV. Expanded-scale Meter displays Are more accurate and the segments light uniformly only if bar mode is used. At 50mV or more per step, dot mode is usable.

This is the important part.....for each 125mV that the input signal increases, a comparator will switch on another indicating LED.


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