Replacing the dashboard plastic PCB

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CJH
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Re: Replacing the dashboard plastic PCB

Post by CJH »

I've been thinking about what I'd do if you came back and said that that's the standard LCD clock module and it protrudes above the plane of the LED housing. I think a better solution might be to split my board in two, to have just the LEDs (and resistors etc) on one board, and then have the connections board stacked on the back of it, using 0.1" board-to-board connectors and 11mm PCB standoffs (like Raspberry Pi 'hats'). There's plenty of depth behind the LED housing (I think - need to check under my dash binnacle), and it would leave the lower centre of the dash clear for whatever people have there.
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Re: Replacing the dashboard plastic PCB

Post by slowcoach »

I don't think that's the stock LCD clock, that looks like something else.. but I'm.sure that can be confirmed.

Sounds like you could do with some more binnacles to test with. They seem to sell for crazy money most of the time though- I got lucky (perhaps cause I'm in kmh not mph) but for £110 I got a complete late one with Speedo tachometer and LCD. My old one was broken in so many places it was just hanging on.
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Re: Replacing the dashboard plastic PCB

Post by CovKid »

AngeloEVS has already made a PCB like this
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Re: Replacing the dashboard plastic PCB

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slowcoach wrote: Sounds like you could do with some more binnacles to test with.

I was thinking the same thing. There are a couple of details I can't tell from my early petrol version - how the buzzer connects, and what the LCD clock housing is like. I don't want to pay silly money for a working late model dash, but I will certainly keep my eyes open for a cheap gash one.

CovKid wrote:AngeloEVS has already made a PCB like this
Yeah, he said. :wink:
I'm targeting a very cheap, flexible DIY kit for those who know which end of a soldering iron to hold, and maybe a (fractionally less) cheap fully built kit for those who don't.
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Re: Replacing the dashboard plastic PCB

Post by CovKid »

Then you only need make the LED board and the connector, plus components with simple wiring diagrams for all the various models. That would keep it as simple as possible. I hard wired mine and made a custom board for the LEDs after testing on veroboard.
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Re: Replacing the dashboard plastic PCB

Post by AngeloEvs »

The clock below the LED display is a standard 52mm Tachometer.

You can use 1/4 W resistors for most of the circuit apart from the Alternator charge circuit LED. The introduction of the horizontal dash connector saw an increase in the Alternator exciter current (doubled in fact). Two 120 ohm resistors are used in parallel, these need to be at least 2W each to handle a max current where V/I = 12.7/60. Tracks need to be bit wider for the alternator LED to pin out on the edge connector. If the ignition is left on without starting the engine these resistors get quite hot. A frequently used method is to to tin the tracks along their entire length to increase the track current capability if track width is a problem.

Same goes for the tracks to the Fuel and Temp tracks, nominal resistance of both guages where coolant temp is normal and fuel tank half full is 100 ohms each, the regulator limits the voltage to 10 so V/I = 10/100 for each track.
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Re: Replacing the dashboard plastic PCB

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CovKid wrote:Then you only need make the LED board and the connector, plus components with simple wiring diagrams for all the various models.

...plus a way to connect everything (multiplug signals, gauges, buzzer, dash lights) to the LED board. I'm with you - that's all I'm doing. I think the multiplug adapter on it's own, with simple screw-down terminals (or the wires could be soldered instead of using connectors), could be useful, even if people approach the LEDs or even the whole dash in a different way. Or the LED PCB could be useful without the multiplug adapter, if people have already swapped the multiplug for something else - again, the wiring will be via simple screw-down terminals.

I'm hoping the bespoke boards will be cheap enough that the finished price (with components) is much closer to veroboard territory than it is to commercial kits.
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Re: Replacing the dashboard plastic PCB

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AngeloEvs wrote:The clock below the LED display is a standard 52mm Tachometer.

You can use 1/4 W resistors for most of the circuit apart from the Alternator charge circuit LED. The introduction of the horizontal dash connector saw an increase in the Alternator exciter current (doubled in fact). Two 120 ohm resistors are used in parallel, these need to be at least 2W each to handle a max current where V/I = 12.7/60. Tracks need to be bit wider for the alternator LED to pin out on the edge connector. If the ignition is left on without starting the engine these resistors get quite hot. A frequently used method is to to tin the tracks along their entire length to increase the track current capability if track width is a problem.

Same goes for the tracks to the Fuel and Temp tracks, nominal resistance of both guages where coolant temp is normal and fuel tank half full is 100 ohms each, the regulator limits the voltage to 10 so V/I = 10/100 for each track.

Excellent - thanks Angelo. Track width for those currents shouldn't be a problem - I use an online calculator to make sure they are wide enough. Some of the boards I've made for my amplifier modules were designed to carry around 20A.
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Re: Replacing the dashboard plastic PCB

Post by CovKid »

Certainly don't hurry this project Chris. With careful thought (and input where it helps) should glean something that is better made than that designed by VW. The ability to use all the potential LED holes a real bonus for those that need extra warning lights. To some extent this is hampered by the existing plug which is why I had to fit an ATX plug/socket but thats not easy to execute without numerous splicing points.
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Re: Replacing the dashboard plastic PCB

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CovKid wrote:Certainly don't hurry this project Chris.

I plan to do an initial prototype order, probably quite soon, to assess any issues/problems and provide feedback to inform the next iteration. There are things I need input on though, such as the pin diameter and pitch on the buzzer PCB connection. I wonder if anyone has a circuit diagram for the buzzer PCB itself - my own van doesn't have that circuit, but since I replaced the original engine with one that has the additional pressure sensor I might consider adding a BOD* if the circuit isn't too complex, and doesn't rely on hard-to-source/expensive bits.

On checking against a spare (empty) binnacle I have here I noticed that the LEDs actually have to sit quite a distance (~16-17mm I think) from the PCB if they're to fill the holes in the panel, so I'm planning to use rigid stand-offs, and it means that the LEDs can't be the type often described as 'short legs' - ~25mm will be required.

* Actually, forget that. Having seen a few photos online the circuit looks quite complex, and I already have an oil gauge, so I won't be adding a BOD. But I do intend to add the connections for the BOD to my PCB, so I'm still looking for details of the pin spacing on the original BOD PCB.
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Re: Replacing the dashboard plastic PCB

Post by AngeloEvs »

Diesel and Petrol models have different BOD circuits which means two separate designs. From a DIY point of view, any mistakes in the assembly and soldering Integrated circuits, transistors, polarised capacitors, incorrect resistor placement, etc, is prone to errors.

I opted to interface to the existing BOD using the original VW connector on a separate PCB, which, along with the regulator socket and LED socket are removed from the membrane and not difficult to do.

All the Dashes I repaired had faulty membranes so these sockets were available and it is not difficult to remove them

I also made the system flexible enough to use the pcb with or without the DOPs or with a enhanced DOPs circuit.

If the DOPs board was not wanted, and some folks (like me) do not like the DOPs system and prefer the more reliable early direct LED to oil pressure switch connection, my pcb has links that can be cut to give the various options mentioned earlier.

Also, LED's today are far more efficient than back in the early '80's and I would opt for higher LED series resistor values than 470 ohms, 1k at least but that is a minor point.
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Re: Replacing the dashboard plastic PCB

Post by CJH »

Thanks Angelo

I was going to revisit the resistor/LED combinations. I quite like the idea of having very bright LEDs for the charge light and the oil warning light, since they need to stand out even in bright sunlight. But the high beam should not be so bright, since it's mostly used at night.

For the DOP circuit, are you saying that the signals to the L-board are different between Diesel and petrol, or only that the L-board circuits are different? My plan was to bring the 6 signals out to screw-down terminals, and then provide a way (e.g. another mini PCB with the correct connector) to connect to the L-board. Are you saying that I would need two separate designs for this approach, or were you simply responding to my stupid idea to remake the L-board PCB (which I've dropped)? Looking at photos of the L-board, it looks like the pins might be 0.2" pitch, with 6 slots out of an 8-way 0.2" connector used. I didn't find such a connector in a quick search, but a 0.1" pitch connector would work. It would be good to get independent confirmation of the pitch of those pins though.

Since my board will have one or two spare LEDs (depending whether the glow plug LED is used) I did consider whether to use one spare for the higher pressure oil switch, but the drawback is that this could legitimately be on below 2000rpm without it being a worry. I think I'll just stick to the oil pressure gauge. But the signals will all be on screw-down terminals in case people want to do something else with them as you suggest.
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Re: Replacing the dashboard plastic PCB

Post by AngeloEvs »

It is the DOPS pcb boards that are different. Both Diesel and Petrol use the same connector but finding a commercially available one with the correct pitch spacing could be a problem.

For the main beam, I use a 5mm standard brightness blue diffused led with a 8.2k resistor to give the correct night and day time brightness or you can use a 3mm white led (or blue) with the original small filament bulb capping left in place and any suitable value resistor.
Last edited by AngeloEvs on 01 Jun 2018, 08:20, edited 1 time in total.
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Re: Replacing the dashboard plastic PCB

Post by CovKid »

Agree with Angelo on resistor values. Important not to overdrive them for longevity. Not sure if this helps, but I completely dismantled the dashlight bulb arrangement when chucking the PCB membrane and found that the dash case only needed very minor filing to accept 10mm LEDs directly in the holes where the bulbs once sat. They fit so well, no hot glue is needed. The advantages over bulbs are well documented and using generic 10mm LEDs makes replacement fairly simple. I'd need to check but I think i settled on a resistor around the 300 ohm mark to give just the right amount of dash illumination with no requirement for a dash dimmer. Mine are on whenever the ignition is on so I never have dark clocks under bridges/tunnels or trees - big improvement.

8k sounds about right for blue LED - lest you want your face lit up like some demonic driver at night :twisted:
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Re: Replacing the dashboard plastic PCB

Post by CJH »

Useful info, thanks folks. I hadn't really given much thought to the dash lights - I thought maybe I'd stop at providing screw-down terminals to wire them into, but of course the kit would be much more useful if it also had suitable bulbs with leads attached. Maybe I'll include a jumper or something to allow them to be always on (like Covkid's) or controlled by the dash dimmer as per standard.

AngeloEvs wrote:It is the DOPS pcb boards that are different. Both Diesel and Petrol use the same connector but finding a commercially available one with the correct pitch spacing could be a problem.

I'm more hopeful than that - if someone has a spare flexible PCB or a spare dash to hand, and can measure the spacing of those pins for me, I reckon something can be made to work.
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