picaxe input voltage

[Shadow1976]

Hi guys,
Quick question. Is it possible to operate a picaxe safely with vss above 5 volts? If so how high can you go?
Regards
Shadow

 

[MPep]

Quick answer, NO. The long answer is to look up the datasheet etc.

Why risk it when a 5V regulator is cheap? Even interfacing above 5V is not difficult.

 

[Dippy]

Not so quick answer...

If you open online Manual 1 (pdf) and then use 'find' function. Insert "5V" and click 'next' it will go to sections concerning power supply.

Click 'next' again and it'll take you to another section. You will find a number of apprporiate sections if you keep clicking. Read thoroughly.
You should be able to find what you want within about 57 seconds which is fairly quick - - but as you haven't logged-in since you posted the question it can't have been all that urgent
Anyway, joshing aside, there are whole sections if you look in the Manual.

For nitty-gritty full (and theoretically more up-to-date) electrical data go and get the apporiate PIC data sheet at microchip.com.

 

[AllyCat]

Hi,

Is it possible to operate a picaxe safely with vss above 5 volts? If so how high can you go?

Do you mean Vss. the normal GROUND voltage? The supply rail is Vdd.

In principle, you can operate with ANY Vss, for example +10 volts (or even 1kV) provided that Vdd is taken to a suitably higher voltage (e.g. +15 volts) and ALL I/O pins are arranged to be "tolerant" of, or compatible with, the external voltages applied or required.

Of course with high voltages you must also consider your own safety, not just PICaxe's.

Cheers, Alan.

 

[Dippy]

I had assumed OP meant Vdd/supply+V and that it was a tuppo.
If Vss is meant then we need some further info.

 

[Shadow1976]

Thanks guys. It was just a question which I know the answer to already. Just wanting to know if anyone has taken one over 5v safely. I do have the manual also. Thanks for your responses.

Not so quick answer...

If you open online Manual 1 (pdf) and then use 'find' function. Insert "5V" and click 'next' it will go to sections concerning power supply.

Click 'next' again and it'll take you to another section. You will find a number of apprporiate sections if you keep clicking. Read thoroughly.
You should be able to find what you want within about 57 seconds which is fairly quick - - but as you haven't logged-in since you posted the question it can't have been all that urgent
Anyway, joshing aside, there are whole sections if you look in the Manual.

For nitty-gritty full (and theoretically more up-to-date) electrical data go and get the apporiate PIC data sheet at microchip.com.

 

[AllyCat]

It was just a question which I know the answer to already.

IMHO the "correct" answer is that the maximum voltage for Vdd relative to Vss is +5.5 volts, with an "Absolute Maximum" of 6.0 volts. The base PIC data sheet gives more details concerning the MR ("input only") pin being 9 volt tolerant, etc., etc..

In practice, it appears that the PIC chips can be quite tolerant of (some) excess voltage, but NOT if that creates a high current and thus damaging power dissipation. However, the pragmatic/simplistic answer is indeed "5 volts is a safe maximum".

Cheers, Alan.

 

[Dippy]

No need for 'humble' and "correct" Alan - you are correct.
For example; many circuits using transformerless mains supplies will have (arguably) 240Vrms-5/3Vish as the Vss (and system ground).
There are too many situations to list... and a prolonged discussion about is for another day.

In hobby battery/DCpsu circuits we just tend to use the simple terms DC0V as Vss and Vdd as the supply+ve.
If people wish to develop other circuits (and their own skills) it's always good to investigate design and use the Manufacturer's data.

It goes without saying (though I will) that people can get good advice here from experinced bods and any real EE who is floating by.

 

[westaust55]

By looking at the Rev Ed PICAXE website pages there are links to the datasheets for the various PIC chips forming the basis of the PICAXE parts. See
http://www.picaxe.com/What-is-PICAXE/PICAXE-Chip-Labels/
From these datasheets the absolute max ( not recommended for continuous operation) and typical operating ranges for the supply voltages are found in the ELECTRICAL CHARACTERISTICS Section of each datasheet.
Absolute maximum voltages:
08M2 Voltage on VDD with respect to VSS, ....................................................................... -0.3V to +6.5V
20M2 Voltage on VDD with respect to VSS, PIC16F1825/9 .................................................. -0.3V to +6.5V
28X2 Voltage on VDD with respect to VSS PIC18F2X/4XK22…............................................. -0.3V to +6.5V

DC Characteristics: Supply Voltage:
This is the normal operating range for chips suitable/capable of a nominal 5 V supply
08M2 == D001 VDD Supply Voltage (VDDMIN, VDDMAX)
&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;.. &#8230; Min 2.3 &#8211; Max 5.5 V &#8230; FOSC <= 16 MHz

&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;.. &#8230; Min 2.5 &#8211; Max 5.5 V &#8230; FOSC <= 32 MHz

20M2 == D001 PIC16F1825/9 &#8230;. Min 1.8 &#8211; Max 5.5 V &#8230; FOSC <= 16 MHz:
&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;.. &#8230; Min 2.5 &#8211; Max 5.5 V &#8230; FOSC &#61603;&#61472;32 MHz (Note 2)

28X2 == D001 VDD Supply Voltage PIC18F2X/4XK22 Min 2.3 &#8212; Max 5.5 V

Hence 5.0 Volt is definitely safe but the chip should operate correctly with a supply up to 5.5 Volts.

With respect to the Absolute Max rratings most Microchip PIC datasheets include a statement along the lines of:

Stresses above those listed under &#8220;Absolute Maximum Ratings&#8221; may cause permanent damage to the
device. This is a stress rating only and functional operation of the device at those or any other conditions above those
indicated in the operation listings of this specification is not implied. Exposure to maximum rating conditions for
extended periods may affect device reliability.

 

[geoff07]

PIC chips (sadly not of the Picaxe persuasion, though it makes no difference) have been known to survive the 9v battery mistake at the school I help at. But who knows what faults are in there just waiting to appear.