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Forum Index : Microcontroller and PC projects : Micromite in a car ....
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| plasma Guru  Joined: 08/04/2012 Location: GermanyPosts: 437 |
Hi, has anyone a working solution for powering the Micromite from the 12 v in a car? i fear resets and other mystical problems. so if anyone have running a pic in his car so please show me your layout for 12v to 5 volt. thx |
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| WhiteWizzard Guru Joined: 05/04/2013 Location: United KingdomPosts: 2934 |
Hi Plasma, I used to design car alarms and can only say that I used plenty of caps on the input and around the vRegs for the simple reason of excessive 'noise' under the bonnet. Typically I used a 9v vReg and a 5v vReg - from memory just the good old fashioned 780x family. This was several years ago, and the MCU I favoured were the 8bit PICs. Since those days there have been many automotive grade power supply chips that have come to market. These may be 'overkill' but you may find a good one that does the job (no experience with these so I can't offer any comments). Hope someone else may be able to shed some more light on dedicated AutoMotive chips for you . . . One final thing, why not quickly build a very simple test unit with 9v & 5v regs + caps, stick on a minimal MM circuit and write a quick program that flashes an LED to show the MM is alive. Ensure OPTION AUTORUN OFF is selected, and don't use any watchdog. Then just put the circuit into the vehicle and leave it running. This test setup won't flatten the vehicle's battery (use CPU 5). Now if the LED stops flashing then you know you have to 'improve' the power supply circuit. If it is still flashing days/weeks later then all is good. You can also use this test no matter what power supply circuit you end up using to ensure it is ok. Things can be added such as a cheap LCD (no backlight) and display the MM's Timer value. This way, if the LED stops flashing, then you get a good indication as to how 'soon' it stopped - this may help pinpoint the issue (i.e. the wipers went on . . . .. ) Good luck! WW |
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| plasma Guru Joined: 08/04/2012 Location: GermanyPosts: 437 |
i cant test it because the car is 300 km from my home. gtx |
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| WhiteWizzard Guru Joined: 05/04/2013 Location: United KingdomPosts: 2934 |
Is the car in 'daily' use? If so, could you ship a 'test' unit to be installed by someone that can then keep an eye on things? Cost of parts would be between 10-20Euros so not too expensive to try. However, you would need to have OPTION AUTORUN ON and then simply add a push switch that starts the flashing LED (and resets the timer if you do an LCD version). I have mentioned this test unit as I am a big fan of getting a working 'test unit' in place as soon as possible - it is a great motivator. 
WW |
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jman Guru Joined: 12/06/2011 Location: New ZealandPosts: 711 |
Hi I have my Micromite Bluetooth interface in the car with NO issues. I also have a PIC 12f509 that auto close my windows with no issues. Lots of decoupling caps Jman |
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bigmik Guru Joined: 20/06/2011 Location: AustraliaPosts: 2949 |
Hi Paul, This has come at the right time for me, I have been arm wrestling with GpS units in my wife's car. They basically never charge and progressively run down till they are flat. I have tried cheap Chinese units and expensive name brands to the same affect. I must have tried 30 different cigarette lighter chargers and modified cables to short the 2 centre pins, solder resistor networks up and down to force high charge rates.. Now the gps units will charge from near flat to full in a few hours with the screen on with them plugged into a mains charger, either iPad charger or Samsung charger.. I am suspecting these ( modern buck switching mode ) cigarette chargers are susceptible to noise from the CAN bus circuitry.. I have searched till I have gone mad(er) for a good old fashioned 7805 based charger.. But they seem to no longer exist.. I intend, next step, to use a rectifier input , lots of filter caps ( the rectifier so the filter doesn't upset the CAN signals) and a well heat sunk 7805 reg.. But of course this will NOT be a small charger... And the wife won't be happy with it taking up most of her valuable lipstick and make up storage space on the console.. If it works I will post back and let you know. Regards, Mick Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<< |
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BobD Guru Joined: 07/12/2011 Location: AustraliaPosts: 935 |
Mick are you thinking that the chargers are the problem? I have no trouble charging my Nokia phones and other gadgetry in the car. Is your car the problem? It detects a foreign body and deprives it of food. Bob |
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| bigmik Guru Joined: 20/06/2011 Location: AustraliaPosts: 2949 |
Hi Bob, I have tried literally about 30 different chargers and cables all to no avail and even an expensive Thermaltake triple output modle that is supposed to be 4.8A and has the iPad style and Samsung and other equipment types of `protocol' to set various charge limits but the bl@@dy thing keeps going flat and shuts down (will shut down whilst driving. I get a max of about .5A on the car chargers (with a WiFi camera in series as well) where as I get .7A charging on a plug pack 240V charger off the mains. I have, of course tried various cables and nothing is quite working.. I suspect as the chargers these days ALL use the `buck' switching IC that it cannot handle the `noise' of the cars power source, the next step is what I mentioned above or power derived directly from the car battery where the noise should be considerably less. I am fairly convinced that it is CAN bus or other interference.. I have tried, unsucessfully, to locate a source of the old style analog cigarette car chargers but they no longer seem to exist. Regards, Mick Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<< |
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| WhiteWizzard Guru Joined: 05/04/2013 Location: United KingdomPosts: 2934 |
Mick, Can I confirm something - are you plugging all these different things that you have tried into a cigarette lighter socket within the car? If so, then first obvious thing is to check the socket is kicking out 12v (ish). Then have you got a 'spare' plug from all your different devices to 'hack' together a simple LED & resistor test circuit that when plugged into the socket will light up the LED. Then make a lead that effectually connects the power to the necessary 'charging' pins on the GPS lead. Now I guess you have tried something similar to the above but I remember when my job involved working on cars that lots of people had 'issues' with their cigarette lights. The most common issue was a 'short' centre pin and hence not making contact (a bit like our cheap breadboards!); the next issue was simply a blown fuse! Then occasionally you came across one that had power, but couldn't drive the intended circuit (possibly what you have). This was resolved by re-wiring a new 'thick' wire from 12v to the socket and including an in-line fuse (typically 3A). Will be interesting to get to the bottom of this one . . . . WW |
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| plasma Guru Joined: 08/04/2012 Location: GermanyPosts: 437 |
hi, at the moment i use a layout with an old fashioned 7805 and some r/c filter . it works until we start the car. if the car on and we plugged in the pic will randomly reset. i fear much spikes and much EM noises here. now i test with 47 myh and a surpressordiode . |
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| bigmik Guru Joined: 20/06/2011 Location: AustraliaPosts: 2949 |
Phil, The current charger has a captive cable and about 1m of lead to a mini USB plug that plugs into the GPS. It also has an inbuilt LED to see that it is getting power.. In fact you are correct that many cigarette chargers pop out and cease making contact, in fact I generally `jam' a couple of cable ties in to hold the charger in place. This one has driven my wife (hence driven me mad) crazy. I will get there when I get around to building a decent supply.. I will prob do it with a largish box, to hold the heatsink and several large caps and if It works build it in behind the dash.. Mick Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<< |
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palcal Guru Joined: 12/10/2011 Location: AustraliaPosts: 1989 |
Don't know if this will help but what about an isolated power supply. I have trouble with my MM based GPS in my golf cart freezing when I operate it with a 48v-12v DC-DC converter. I purchased an isolated power supply 10v-16v in and 12v out only to find it would not supply the necessary current so searching for another one. Then again maybe filtering on the 48v, side may help. Paul. "It is better to be ignorant and ask a stupid question than to be plain Stupid and not ask at all" |
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| Frank N. Furter Guru Joined: 28/05/2012 Location: GermanyPosts: 947 |
Hi Plasma, we developed in a former job electronics for cars and caravans. Try a current compensated choke (there are very small ones available from Würth ) - it makes wonders! It is more better when you use a pi-filter after the choke... Frank |
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| aargee Senior Member  Joined: 21/08/2008 Location: AustraliaPosts: 255 |
It really does help if you put a 1W 16-18V Zener across the 12V supply (Cathode to +, Anode to -). This takes out a lot of the nasty high voltage spikes running around the cars electrics. For crying out loud, all I wanted to do was flash this blasted LED. |
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