Re: ADC0804 negative voltage
Yes, its possible.
But this would lower down the 8-bit resolution. You leave ref/2 pin open, don't connect it. If I remember that PIN number correctly, in this you get range from 0-5V.You first takes the absolute value of -5V to +5V, so altogether difference of 10V, means if you give negative voltage, it must be get convert into positive value, if you get positive value it remains the same, now suppose you get scale from 0V to +10V, 0V represents -5V and +10V represent +5V.Scale it down from 0-10V to 0-5V. Now then feed it into your ADC0804. All is done now.
Remember:
1)Add +5V in input, you get range from 0-10V.
2)Divide the range 0-10V with 2
3)Fed the result into ADC0804.
ADC0804, won't know what it means, you will be the one, who must understand what the values means.From 0-2.5V, this means range from -5V to 0V. From 2.5V to 5V means 0V to +5V