Author Topic: analog input protection  (Read 9702 times)

Offline z0tya

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analog input protection
« on: January 27, 2010, 09:15:34 pm »
Is it possible to use this (max 366) for saving vems analog input pin against overvoltage?
http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1084

Offline SamSpade

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Re: analog input protection
« Reply #1 on: January 27, 2010, 11:02:35 pm »
Short answer is no.

For resistive sensors like CLT thermistors and TPS, it will give a totally wrong reading since the chip introduces a resistance in series.  For active sensors like MAP sensors, the chip will clamp the output above GND and to just 3.5V (+5V - 1.5V).  Most MAP sensors (and VEMS) use the full range of 0-5V for the pressure values.

Which inputs did you want protected anyway?

Offline rob@vems.co.uk

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Re: analog input protection
« Reply #2 on: January 28, 2010, 02:06:24 pm »
I'm guessing he means the ALS/Launch inputs.

Offline Denmark

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Re: analog input protection
« Reply #3 on: January 28, 2010, 03:05:31 pm »
Does it matter, if All that The switch is conneted to is Ground, you only need protection if you plan to run something other then a grounded swith

/Skassa
working on the boxer

Offline z0tya

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Re: analog input protection
« Reply #4 on: January 28, 2010, 06:21:31 pm »
for example vr sensor for wheelspeed

Offline rob@vems.co.uk

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Re: analog input protection
« Reply #5 on: January 28, 2010, 08:28:29 pm »
That would need something like a LM1815 chip and some pull-down resistors.

Offline SamSpade

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Re: analog input protection
« Reply #6 on: January 29, 2010, 05:09:41 pm »
Yes, the LM1815 Adaptive Variable Reluctance Sensor Amplifier is the proper way of interfacing with a wheel speed sensor, the same way VEMS does it.  In fact you can use the 2nd LM1815 (U12) on the board if you had it installed but don't use it for camsync.

Offline z0tya

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Re: analog input protection
« Reply #7 on: February 01, 2010, 02:33:14 pm »
Yes, the LM1815 Adaptive Variable Reluctance Sensor Amplifier is the proper way of interfacing with a wheel speed sensor, the same way VEMS does it.  In fact you can use the 2nd LM1815 (U12) on the board if you had it installed but don't use it for camsync.

Wow it's a great idea, my vems config is vr/vr and i run wastedspark now, so the 2nd chip is usable.
Can you write how can I use it? Maybe with pics :)

Thx

Offline SamSpade

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Re: analog input protection
« Reply #8 on: February 02, 2010, 08:04:57 am »
If you can take a high-res photo of your board I can figure out what changes (resistors, jumpers, etc.) you need to do.  Just need the part of the larger yellow box below.  The 2 LM1815 are the ones boxed.  The lower box are the jumpers.  We may have different jumper settings so it's best we see how yours is set up.




Offline z0tya

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Re: analog input protection
« Reply #9 on: February 02, 2010, 02:24:59 pm »
Thanks!

This the best photo what I have now. Maybe good...
http://www.cosworth.hu/misc/myvems_top.jpg