Is it possible to read an analogue input and then output double the voltage on another pin. and the input voltage can be between 0.4v and 4.4v?
If you’re just using an AVR Arduino you will need something else to output the voltage.
What’s the application there maybe an easier route?
What’s the Board?
AVRs can't output analog voltage.
No. The maximum output voltage on any pin is the processor supply voltage (usually 3.3V or 5V).
Such output could be produced using a 0 to 10V DAC module.
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sorry i should have explained it a little better - the output will never be over 5v but the input will be between 0.4v and roughly 2.2v so the output needs to mimic the input but be double so will go from 0.8 to 4.4v... for a peddle sensor in a car
An op-amp in non-inverting configuration with a gain of two is a simple solution that avoids the need for a DAC.
Thanks robertnc and Delta_G and also the others above a very big help... will look into it and see how i go.... once again thank you 
messed around with the OP-AMP idea (LM324N) and it works perfect upto a point... the circuit is running off the 5v and 0v the sensor signal is coming from... at 82% of the movement the input voltage of the sensor continues to rise but the output voltage stops at the 82%... is this something to do with the type of OP-AMP or is it a limiting factor of the voltage the unit is running off?
The LM324 is not a "rail to rail" op amp. If you check the data sheet, you will see that the maximum output voltage (VOH) is specified to be a couple of volts less than the supply voltage.
Choose a rail to rail op amp instead, but keep in mind that the output can supply very little current when it is at the maximum possible voltage.
Or, use a higher voltage supply for the op amp (e.g. 7-9V), then it can reach 5V output. Make sure not to exceed the allowable input voltage for anything connected to the op amp output.
ah ok... current shouldnt be an issue and the supply is 5V and i need it to get to roughly 3.65v ... so now to try and find a rail to rail op amp
I like the MCP6001, but it is slow and intended for very low power operation. Great for use in sensors!
I'm with @jremington but I prefer to go for dual op amps (2 in 1 package, often for the same price, and sometimes better availabiltiy) so I'd choose the MCP6002.
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