For a project I'm working on I could use a voltage reference, of around 1.5-2 volts, maybe a tad less, the exact voltage isn't as important as that the voltage stays relatively stable even if the supply voltage or temperature changes.
The circuit has a 78L05 to power a PIC and I'm using a voltage divider to create the reference voltage from the Vdd. This works fine, as long as Vdd stays constant. But if Vdd changes, say due to a weak battery or because I'm testing and powering the circuit with my Pickit 2, my reference voltage changes as well, which throws off my A/D conversion accuracy.
I know that there are voltage reference ICs I can use. And there's zener diodes. Unfortunately, the only zeners I have are 5.1V, and RadioShack doesn't sell any lower-voltage zeners. They don't sell reference ICs either. I don't really want to order online just for one part (my wife's getting tired of all the packages from Mouser as it is).
So, excluding dedicated IC references and zener diodes, how can I create a reference voltage using run of the mill parts that is reasonably stable? Maybe using the voltage drop of a silicon diode? I measured some of my diodes and the drop seems to vary from one to the next, from 0.55 to 0.65 volts typical. Plus, I don't know how stable the voltage drop of a given diode is. If it varies too much once the firmware is calibrated, it can throw off my readings.
Any other suggestions?
The circuit has a 78L05 to power a PIC and I'm using a voltage divider to create the reference voltage from the Vdd. This works fine, as long as Vdd stays constant. But if Vdd changes, say due to a weak battery or because I'm testing and powering the circuit with my Pickit 2, my reference voltage changes as well, which throws off my A/D conversion accuracy.
I know that there are voltage reference ICs I can use. And there's zener diodes. Unfortunately, the only zeners I have are 5.1V, and RadioShack doesn't sell any lower-voltage zeners. They don't sell reference ICs either. I don't really want to order online just for one part (my wife's getting tired of all the packages from Mouser as it is).
So, excluding dedicated IC references and zener diodes, how can I create a reference voltage using run of the mill parts that is reasonably stable? Maybe using the voltage drop of a silicon diode? I measured some of my diodes and the drop seems to vary from one to the next, from 0.55 to 0.65 volts typical. Plus, I don't know how stable the voltage drop of a given diode is. If it varies too much once the firmware is calibrated, it can throw off my readings.
Any other suggestions?