looking for someone who knows there electronics

[thrash-boy]

im planning on making one of these for my datto to replace the old analogue clock that is crap, inaccurate and no longer works.

 

it is a LED Bar graph tachometer circuit diagram i found after countless hours of looking everywhere on the internet.

 

 

 

the only thing i understand about it (because im not very good at understanding how circuits work just by looking at the diagram) is that it has a frequency to voltage converter that converts the frequency the coil discharges (when a plug fires) to a constant voltage, which in turn drives 2 (yes 2) LED bar driver chips which make the lights light up.

 

Looking at the description the RPM range can be changed by adjusting one of the resistors and capacitors.

 

 

 

a better quality (and slightly different?) version of the diagram can be found here: http://www.t-r-j.com/Auto/Tach/tachometer.htm

 

 

 

What i would like to know first of all is someone to confirm that if i go and buy the bits tomorrow (not that i will until im sure everything ok) it will work.

 

 

 

i would also like some advice on what to actually build it on. i dont have the equipment to make my own circuit boards (the special pens and acid bath thing) but if its worth it and doesn't cost to much i would consider buying one. what else could i mount a project like this on?

 

I do have several electric soldering irons and a multimeter if that comes in use.

 

 

 

about positioning it: looking at the diagram the led's are being fed a constant 6 volt supply, and the chip just earths the led to make the light come on. if this is the case it should be fine to mount the power supply bit and leds right behind the dash, and mount the chips and the bits that actually make it work in a separate location within the car.

 

i shouldn't be troubled by lights that don't shine very bright because of the resistance from the long lengths of wire that power the leds, like i would be if i mounted the entire thing somewhere else and just the leds behind the dash?

 

 

 

EDIT: opps meant to hit preview. anyway thanks for all the help in advance! :)

[ClareJonsson]

May I ask, have you ever used a soldering iron before?

[thrash-boy]

May I ask, have you ever used a soldering iron before?

 

yes a few times actually.

 

ive done a bit of soldering on cars at home various times, and a hell of a lot at school last year and the year before. the 2 major things ive made was first a mine game where you jump 1 nail at a time through a field of nails, and there are 3 leds that tell you if your safe/nearing a mine/or you have hit a mine and lose. the ideas to work out the path and make it to the otherside of the board. kind of hard to explain.

 

the second one was a double electronic dice. you push a button and it generates 2 random numbers (1 to 6) and displays them on 2 sets of leds (eg if you get 1 it lights up 1 led, you get 2 it lights up 2. it makes 2 different numbers). i have no idea how it worked but it involved making 2 silicon board things, drilling holes, and soldering in a hell of a lot (in my view, probebly hardly any for someone greatly experienced) of small components.

 

 

 

ill post some pics later if i get round to it.

[ClareJonsson]

Okay, then you could probably make this using vero boards :)

 

 

 

You just need to map out the circuit!

[Deathmath]

And mapping can be hard if you've never done it before, try not to mess up. :lol:

[thrash-boy]

untill now i never knew what veroboards were lol. sounds like a good idea.

 

do all ic sockets fit into the holes of all vero boards? or do i have to make sure i get one with the holes the right distance apart?

[ClareJonsson]

untill now i never knew what veroboards were lol. sounds like a good idea.

 

do all ic sockets fit into the holes of all vero boards? or do i have to make sure i get one with the holes the right distance apart?

 

Yes usually IC sockets are the right size for veroboards, I would also get a track cutting tool too as it's much easier than cutting the tracks with a knife etc.

 

 

 

I would also heed Deathmath's post and map it all out way before you start soldering anything, you really need to make sure tracks are cut and any loops between tracks are mapped. If you don't do this you're gonna end up with a right mess. Also if you are not too happy with soldering I would practice a bit on soldering bits of wire into spare veroboard offcuts.

[thrash-boy]

ok thanks for the advice.

 

tomorrow ill start mapping it out on graph paper with a pencil and eraser (found the idea of google) until i work it out and everything fits.

 

when i do go ahead and buy it ill use some scraps to practice soldering on the veroboard as you recommend.

 

ive made a easier to read list of all the bits, you can see it here if you feel like making sure i haven't missed anything. if you dont want to thats alright, im fairly sure i didn't miss anything. Note: the plugs and wire are so i can mount the leds in the instrument cluster after i remove all the clock remains, and the veroboard bit somewhere where theres a little more room.

[ClareJonsson]

Good luck, if it all works can we see pics of the finished project?

[thrash-boy]

Good luck, if it all works can we see pics of the finished project?

 

sure

[thrash-boy]

ive came up against some more problems lol.

 

I need to know:

 

 

 

-Im having trouble finding a 1uF 50v tantalum capacitor. could i instead use a Electrolytic one? does it have to be 50v or could it be higher?

 

im guessing this one would replace it no trouble (does 50 wv mean 50v with these type of capacitors)?: http://search.dse.com.au/search?w=R4295

 

or maybe even this one (450v instead of 50v though)? http://www.jaycar.com.au/productView.asp?ID=RE6034

 

It is for C1 on the wiring diagram linked to above. it description says its to isolate the tach input from the +12V dc on the coil.

 

 

 

-EDIT: re-reading my questions i typed over an hour ago Ive since answered this one on my own. i found one exactly the same on the other website.

 

 

 

-with the 100k variable resistor (R3 on diagram) im assuming double gang means you can connect 2 things to it. i would only need a single gang right?

 

 

 

-im assuming by 2K2ohm they mean a 2.2k (2200 ohm) resistor (R5 and R6 on diagram)

 

does it matter thats it 1/4watt instead of 1/6w? the tolerance is the same

 

-http://search.dse.com.au/search?w=R1082

 

 

 

-the rectifier diodes on the circuit are all used for protection. the one listed in the part list is a 1a 50v. i can only find a 1a 1000v. so could i replace this:

 

http://search.digikey.com/scripts/DkSea ... 001MSCT-ND

 

with this:

 

http://search.dse.com.au/search?w=Z3207

 

 

 

-The digikey part number P4251-ND doesn't exist (or so there website says). the part is listed as a 0.047 uF capacitor. it has 2 functions (there are 2 in circuit):

 

1. suppresses multiple counts from voltage overshoots

 

2. storage capacitor - increasing its value decreases the RPM range

 

looking at the diagram to see what its hooked up to may help.

 

what capacitor should i use that would preform the same function? could you post a link to one please?

 

 

 

-i think ive asked this question earlier. could i replace the capacitor labeled C4 in the diagram with a higher voltage one? i cant find a 16v volt version but i have found a 35v one, otherwise exactly the same.

 

ie use this:

 

http://search.dse.com.au/search?w=R4720

 

instead of this:

 

http://search.digikey.com/scripts/DkSea ... e=P2105-ND

 

 

 

-i cant find any frequency to voltage converter ics at all on the 2 websites ive been using. ive found 1 bar graph driver (http://www.jaycar.com.au/productView.asp?ID=ZL3914). is that the same as the one in the diagram? looking at the pins on the diagram above and this, which is linked to at the bottom of the description of teh driver on the jaycar website, they apear to be the same thing. all the pins appear to have the same function, so im assuming it would work.

 

i hope they can order in the other ic's, and the led drivers if thats not the right one.

 

 

 

thats my long list of questions lol. if anyone has any answers it would be much appreciated!

 

im off to plan my veroboard now, even though i was going to do it hours ago lol.

[thrash-boy]

one final question and once i work out ansewr to the above questions, i should be good to go :)

 

heres that final question:

 

The variable resistor doesn't make much sense to me in the diagram. i cant work out which pins of the resistor connect to which bits on the diagram.

 

heres a picture trying to explain what i mean, along with my almost complete plan (Diodes and capacitors may be in the wrong way around, i havnt worked all that out yet. this is just planning how much board i will actually need and where everything will fit.)