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Forum Index : Microcontroller and PC projects : Micromite 28 pin in car
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| RyanHammond Newbie  Joined: 29/03/2018 Location: United StatesPosts: 15 |
Hello forum members, I would like to use the micromite 28 pin chip in a project that will be installed under the hood of a car. Is there anything I should be worried about as far as the power is concerned? I was thinking about using the LM2937 3.3 voltage regulator to get the 3.3v for the micromite and rest of the circuit, but should I add anything else other than the recommended filter capacitors? I've heard that cars have notoriously bad power and not sure if I would be better off using a usb cigarette lighter type power supply and run the cable to under the hood (not my first choice...) or if a better source for 3.3v is available. Any ideas would be appreciated. |
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| WhiteWizzard Guru  Joined: 05/04/2013 Location: United KingdomPosts: 2944 |
All I would say is don't forget to be wary of heat too! The bonnet can experience extreme variance of temperature so it depends on what you are trying to achieve - do you need 24/7 operation of your MM? OR is it only when ignition is on? Assuming a 12v vehicle, then there are many options for dropping to 3v3. I would strongly recommend too that you use the WatchDog feature within your software. Cars are notoriously noisy - especially when engine is cranking to start. With good smoothing caps, and watchdog timer then you should be just fine . . . . WW |
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| JohnS Guru Joined: 18/11/2011 Location: United KingdomPosts: 4044 |
Possible sudden drenching with water, too. Even icy water if you live where that happens. The water may well be full of contaminants (such as salt, if icy). John |
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| matherp Guru Joined: 11/12/2012 Location: United KingdomPosts: 10315 |
I add a diode in the +ve supply and a TVS between the rails after the diode that will keep any spikes below the max voltage of the regulator |
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lew247 Guru Joined: 23/12/2015 Location: United KingdomPosts: 1702 |
What's a TVS? |
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TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 6283 |
Transient Voltage Suppressor Like a very fast acting zener diode. Jim VK7JH MMedit |
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| RyanHammond Newbie Joined: 29/03/2018 Location: United StatesPosts: 15 |
Wow, thanks for all the suggestions. I have not heard of a TVS, but that sounds like it is a good idea for the car power. I will do a bit of research on this. The unit will only be powered while the car is on so I will hook up to an accessory power line. It will also be in a case to keep it dry. Thanks again. |
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| WhiteWizzard Guru Joined: 05/04/2013 Location: United KingdomPosts: 2944 |
IF you are to mount the case under the bonnet then I'd advise one of two things: 1> Use potting compound - water will sure find its way into an enclosure over time. And the extreme temperature variations can lead to 'warped' casings (i.e. gaps opening up) 2> Reconsider placing the case inside the car (most likely to remain dry in there!) |
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| Frank N. Furter Guru Joined: 28/05/2012 Location: GermanyPosts: 949 |
I use normaly one of these SMBJ TRANSIL DIODES. Frank |
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CaptainBoing Guru Joined: 07/09/2016 Location: United KingdomPosts: 2170 |
I would use a sealed box packed with vermiculite - you can get it from garden centres or stove shops no problem. High temperature and great insulation. https://en.wikipedia.org/wiki/Vermiculite The seal to keep out moisture and the vermiculite to keep out heat. Works really well on my beer barrel sterilization monitors. They go through an autoclave inside a barrel and are un-affected by 132C for 15 mins. I don't monitor the temperature inside the enclosure but I have to monitor the external for the certification process and the module has to be part of it so its exterior is also sterilized by the heat. hth |
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panky Guru Joined: 02/10/2012 Location: AustraliaPosts: 1114 |
Ryan, I would also strongly recommend an intermediate voltage reg along the lines of an LM317 variable reg to take the voltage down to somewhere between 5 and 9 volts into the 3.3 reg for the micromite - the reason for this is that under some charging conditions the voltage from the car alternator can get up into the 14 volts area - this is a big differential to feed into the 3.3v reg. It also adds a buffer for interference. panky. ... almost all of the Maximites, the MicromMites, the MM Extremes, the ArmMites, the PicoMite and loving it! |
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| JohnS Guru Joined: 18/11/2011 Location: United KingdomPosts: 4044 |
Some do smart charging and can be well over 15V. John |
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| RyanHammond Newbie Joined: 29/03/2018 Location: United StatesPosts: 15 |
It looks like the LM2937 3.3v regulator handles the automotive spikes pretty well according to the data sheet. I may still put a tvs across the power anyway just to be sure. At this point, the case may well wind up inside the car for a bit of added protection. |
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