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domwild
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Joined: 16/12/2005
Location: Australia
Posts: 873

Posted: 01:33pm 28 Aug 2014

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Hi,

Sorry for monopolizing this forum. My old Motorola phone charger outputs a listed 4.4VDC, which I might use for the Picaxe. It outputs 4.48VDC on the meter.

1. How stable is such a supply as I do not want to feed this Vcc back into the Picaxe to cross check it before using it in the Amp calculations via the Allegro?

2. Red and black wires give me the 4.4V, there are two more wires, yellow and green. Any idea what they are being used for?

dom

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Downwind

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Joined: 09/09/2009
Location: Australia
Posts: 2333

Posted: 03:56am 29 Aug 2014

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Is it a USB socket on the end of the charger (as i well expect it is by the wiring you list)

Yes you could use a 4-5v supply, but personally i would not, and would use a voltage reg to reduce a higher voltage to 5 volts.

The reason is all ADC readings are referenced to supply voltage, and should your supply voltage fluctulate than so will your readings, so best to create a stable supply voltage and get reliable data from all readings.

You quote 36 volt supply in another thread, a LM317 voltage reg could handle that input voltage and give a stable 5 volt output, so its the sort of thing i would be looking to use.

Pete.

Sometimes it just works

domwild
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Joined: 16/12/2005
Location: Australia
Posts: 873

Posted: 12:48pm 29 Aug 2014

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Thanks Downwind. It is an old charger, which is not USB and therefore not 5V but only a measured no-load 4.48V. I suppose it could go up and down with mains voltage unless it is already limited internally.

Am just thinking of using it during program establishment, rather than picking it up from the battery. Picaxe UK also supplied a battery pack for the proto board, so I can use that, but even that would not be a stable Vcc.

Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up.

Winston Churchill

Goeytex
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Joined: 12/05/2014
Location: United States
Posts: 74

Posted: 10:56am 07 Sep 2014

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If you are using ADC with a Picaxe, many Picaxe chips support ADCCONFIG and FVRSETUP commands.

With these commands you can set the ADC +V reference to the internal Fixed Voltage Reference. With a 5V supply this can be wither 1.024,2.048, or 4.096V.

With the ADC reference set for 2.048 or 4.096 supply fluctuations will not affect the ADC reading. The cost is having to use a voltage divider for the input, but this is only two resistors that can be easily calculated.

Supported Picaxe Chips are all M2 chips and 28/40X2.

domwild
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Joined: 16/12/2005
Location: Australia
Posts: 873

Posted: 12:52pm 07 Sep 2014

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Thanks Goeytex. My old Picaxe I resurrected is only a 28X, next PIC I get will have floating point, proper ADC and many other goodies.

Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up.

Winston Churchill

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