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Forum Index : Microcontroller and PC projects : Maximite Power Up Problem
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Nick Guru  Joined: 09/06/2011 Location: AustraliaPosts: 512 |
My new Altronics Maximite is exhibiting the same problems my first one did. 50% of the times I power up, it goes into Firmware Program mode with the LED flashing. Eventually it will power up fine and operayte flawlessly. Seems to me some problem with these Altronics kits. What worries me, is that my first one that did this, eventually got to the stage where it din't power up at all. Ideas? Nick |
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MicroBlocks Guru Joined: 12/05/2012 Location: ThailandPosts: 2209 |
Power supply not stable enough would be my first guess. You can try a battery pack, like 4 new AA batteries in series. Can not get more stable then that. It will allow you to establish if it is a power supply problem. Microblocks. Build with logic. |
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jebz Regular Member  Joined: 13/06/2011 Location: AustraliaPosts: 79 |
A while ago I was having trouble with a PIC project not starting smoothly and becoming random. I traced it to a compact switch mode multi-voltage plugpack that had too much noise on it's output. On a CRO it didn't look like much but as soon as I swapped to a linear old style plug pack everything came good. |
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| MicroBlocks Guru Joined: 12/05/2012 Location: ThailandPosts: 2209 |
Maybe another cause is that the reset circuit is a little bit to quick to release the reset line. I always use supervisory chips for that. I would have to look at the schematics, you might be able to add a small resistor or capacitor to make that reset line better at startup conditions. How do you switch the CMM on and off? If you switch of the power supply or pull the adapter out of the wall socket it might be that the power supply is having 'startup' problems. Those problems can then enter the CMM and cause further problems. If that is the case you can add a capacitor to the output of the power supply. You can use a power up sequence by first powering up the power supply and then connect it to the CMM. Microblocks. Build with logic. |
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| Keith W. Senior Member  Joined: 09/10/2011 Location: AustraliaPosts: 118 |
Hi Nick, I have an Altronics Colour Maximite Kit and had problems when powered from USB. Particularly I had problems with communicating via USB to Terra Term. I posted about this at the time. You are keen on games. Do you have a joystick or something drawing power from the Maximite? This problem is not particularly caused by Altronics version. I am tempted to remove both Schottky diodes from my Maximite and replace them with a switch to select between USB and External power. The diodes drop the voltage a little. I prefer to use an external 9 volt DC plug pack. Much more than 9 volts and the 5 volt regulator warms up. With the Schottky diodes in circuit there is less than 5 volts on the nominal 5 volt supply which may not be sufficient for any 5 volt external devices drawing power from the Maximite. As you are going into program mode, I think that I remember someone (Geoff?) suggesting a pull up resistor on the wire from the programming select button? Is the button and track clean? Without a pull up resistor it may not require much leakage to hold this line low. Or perhaps your power supply is slow in reaching correct voltage? Hope you find your problem. Keith W. |
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CircuitGizmos Guru Joined: 08/09/2011 Location: United StatesPosts: 1425 |
I suggested the pull up be tried as an attempt to see if that is the problem. I do include the pull up resistor for the CGCOLORMAX. Micromites and Maximites! - Beginning Maximite |
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| Nick Guru Joined: 09/06/2011 Location: AustraliaPosts: 512 |
Thanks for the tips. I think I found the culprit! My power adaptor! I have been using the same power adaptor that powered my original B/W Maximite. This adaptor worked perfectly and I continued to use it on my Colour Maximite. It's a simple transformer based adaptor providing 7.5 volts at 1 amp. I swapped it for a 9 volt 300 ma power adaptor last night and now my CMM is powering up every time. So, I assume that the CMM's startup circuit is designed with 9v in mind. Also, maybe the 1 amp supply is what put stress on some part of the circuit (regulator) and that's what fried my original CMM? Anyway, appears to be happy days ahead. Nick |
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| CircuitGizmos Guru Joined: 08/09/2011 Location: United StatesPosts: 1425 |
No. The CMM would only draw what it needs, not 1 amp. You could have a 9V 1000 amp supply and the CMM wouldn't draw 1000 amps, just the 100s of milliamps it needs. If it did pull 1000 amps you would have vaporized metal right quick... Micromites and Maximites! - Beginning Maximite |
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BobD Guru Joined: 07/12/2011 Location: AustraliaPosts: 935 |
It is the 7.5 volts that was always the problem. It is insufficient to allow for voltage drops across a diode and the regulator and still produce 5 volts at the output of the regulator under all conditions. Variations in loading could cause the intermittency of the problem. IIRC a 9 volt supply was the original spec. It is a common misconception that a supply with higher current capability than the load needs will cause problems. However, a supply must be capable of providing enough current to satisfy the load. CG said it very nicely. |
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| BobD Guru Joined: 07/12/2011 Location: AustraliaPosts: 935 |
Nick, I almost missed this. Your new power supply of 9V 300mA may also be intermittently inadequate. I couldn't put my finger on it when I wrote the previous post but after a shower, shampoo, shave and a sh.., it hit me. The Maximite needs about 150mA and a keyboard can use up to about 200mA depending on the keyboard + audio + joystick and this is all coming from a 300mA supply. Your supply is probably not good enough for this load. The supply that Altronics suggested for the original MM was 9V DC 670mA and this had plenty of margin to drive the MM and many (but not all) of the gadgets that could be attached. Altronics 9V DC 0.67A plugpack M9237B It comes with a 2.1mm reversible plug. The MM thoughtfully includes a diode to protect against people getting the polarity the wrong way round and destroying components. |
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| Nick Guru Joined: 09/06/2011 Location: AustraliaPosts: 512 |
I got excited too quick there. It still does exhibit this startup problem but not as often. Usually from a cold start (off for awhile). I turn the power off to the plug pack when I switch off the CMM. I will try leaving it on to see if that makes any difference. Nick |
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