Hi thanks for your replies
Yes Tex that is what I'm saying!
I have a 100nF in parallel with a 10uF ceramic as close as practically possible to the power pins of a PICAXE.
Sometimes I have rather long tracks on the power lines of my PCBs (~4") and therefore place the 10uF capacitor accross the power pins of the PICAXE to act as a small resevoir.
Rick
This is excellent design practice. A farad is a farad, whether it is electrolytic or ceramic. The benefits of modern high capacity ceramics include:
1) They are small
2) They (usually) have a lower Equivalent Series Resistance (ESR) than an electrolytic
3) They are (usually) less expensive than an equivalent tantalum electrolytic
4) They are somewhat forgiving of short term reverse polarity
5) They tend to have better wide range temperature characteristics
6) They tend to have a longer lifetime, and tend to fail open, rather than shorted like an electrolytic
7) In surface mounted packages, they tend to have a higher self resonant frequency (SRF) due to the small size and lack of wire leads, so they tend to function better as high frequency bypass devices than the equivalent leaded tantalum. They should not be used as high frequency by-pass, but they generally don't hurt, unlike large leaded electrolytics (especially aluminum).
Drawbacks:
1) They can get really expensive in large values. REALLY expensive.
2) They are not as tolerant as tantalum electrolytics of excess temperature during soldering
The use of bypassing is a science that devolves into an art with more experience with circuit design. If you have very high current devices (many pulsed LEDS, motors, many fast switching digital devices) a local 10 nF and 10 uF at each IC package is a very good idea, with massive (>100 uF or more) directly at the high current devices.
Keep in mind that there are nuances to this. For example, many linear voltage regulators cannot tolerate a short on their input if they have more than about 25 uF on their output, (voltage dependant) since the caps discharge backwards through the regulator. This varies by device, and there are design methods that can (and should) be employed in such cases.