Datasheets don't seem to specify electrical data

[Katzenjammer]

I'm a utility cyclist trying to become car-free, and I ride my bike regardless of time or weather. To help make that easier and safer, I'm kludging up a design for a comprehensive picaxe-controlled lighting system. I'm a software nerd, but my hardware knowledge is extremely limited, one might even say nonexistent.

So I'm trying to discover what the picaxe expects to find on its input pins by way of voltage and current, and what it similarly puts out onto the output pins. But none of the datasheets appears to include that information. It seems fairly basic, so maybe it's a case of "every fule know" and I'm just the wrong kind of fule.

If someone can point me to the information, ta muchly.

 

[Matt_C]

I would look at section 1 page 47 of picaxe_manual1.pdf.

 

[slurp]

I guess the answers are in the Microchip documentation for each of the chips.... it would be a large cut'n'paste to put all that stuff in the Picaxe manual!

best regards,
colin

 

[Technical]

So I'm trying to discover what the picaxe expects to find on its input pins by way of voltage and current, and what it similarly puts out onto the output pins

The supply voltage is the answer.

Therefore if you run at 5V, for an input, logic high is 5V and logic low is 0V. In practise between 0-0.6V is good for low, about 3V and above for high. In between is no-mans land and could go to either. Current is negligable as it a high impedance input, the voltage is the important factor.

On outputs you get 5V (near enough) when high and 0V when off. Max current capability is 20mA sink or source.

 

[Katzenjammer]

Ah, many thanks to all. T's info is exactly what I was looking for.

K.

 

[jacobbiljo]

On a similiar note I am confused about the permissible supply voltages for an 18X and picaxes in general. Reading the Pic datasheet it says that I can apply up to 7 volts to the chip but the picaxe site suggests a max of only 5.5 volts. A Nuts and Volts magazine article from january of this year said not to use 4 AA batterys which would apply 6 volts to the picaxe because it could instantly fry the chip. The supplied circuit diagrams of the prototyping boards show a label of 6 volts on the input terminal to the board. I followed this circuit exactly and my board does not seem to work. There is so many conflicting words on what the maximum voltage is and id just like to be told for sure. Im worried that i have infact fried the chip, as i in fact followed what picaxe has recommended the board be powered by, following there own circuit.
thanks for any help
Jacob Botden

 

[moxhamj]

My personal preference is a 5V regulator as all the analog input values then can be accurately referenced off this. The other option is 3 AA batteries =4.5V. I haven't tried going above 5V - maybe you can get away with 4 normal AAs but 4 rechargeables can be well over 1.5V per cell when they have just come out of the charger.

 

[jacobbiljo]

Thanks for the opinion. my problem is as of right now the picaxe isnt communicating with the computer so im guessing it might be broken. What is complicating my troubleshooting is that this is the only Picaxe i have and the only board to program it in so i have no means of comparison to see if it is the pic or the circuit that is not operating correctly. I was trying for a definate yes or no to know if the board is fault or if in fact i have destroyed the picaxe.
The line following competition which this is entering into starts on friday so its starting to be nail biting time.

 

[moxhamj]

I know this isn't much help but I tend to keep at least 10 spare picaxes on hand (they go into projects pretty quickly) so it is easy to check if a chip is zapped. Do you have a supplier that can get one to you in a few days? (We are lucky in Australia as suppliers like microzed will deliver an order the next day by express post).

 

[hippy]

@ jacobbiljo : The 7.5V limit is the absolute maximum, beyond which you can be fairly certain damage to the chip will occur. The maximum operational supply voltage ( D001 in the datasheet ) is 5.5V. Above that there's no guarantee of correct operation of the chip. Most times the chip will work at 6V and no damage should be caused, but because that's above the maximum operational rating it's not recommended. "Instantly fry the chip" is highly unlikely at 6V. Connecting 9V or the battery the wrong way round has very good odds of instantly frying it.

For the 18X, the definitive answer is probably along the lines of ... Between 4V and 5.5V you should be fine. Below 4V it may work but may not and is not recommended ( other PICAXE variants will work properly below 4V ). Between 5.5V and 7.5V it may work but may not and is not recommended. Above 7.5V and you are likely damaging your chip and must be avoided.

The problem you are having is probably not power supply related but make sure you're using new batteries, and try with just 3xAA, 4.5V.

If you've build your own board, check you don't have missing wires, shorts and wires crossed over, particularly for the download circuit PC connection, and note the download circuit is not a voltage divider. For the 18X, mae sure the 4K7 pull-up for reset is connected.