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[1] Basic Electronics

----------> >--- | | Check the V(open circuit) of the |----| | solar cell. Let's presume 24.0V. | | / Change the value of R1, beginning | \ | R1 \ with a high value. You say this | /\ | / is a big cell, so we'll try 1K. | | \ If the V(load) is still 24V-ish, |----| | try with a smaller resistor. | | As we lower the resistor value, ----------> >--- we are increasing the load. At some point the voltage V(load) will sag to some lower value. That shows you the limit of compliance of the solar cell. If we say that 90% is our limit then we will stop testing when we reach 21.6V. So, now we have a resistor installed that drops the V(load) to 21.6V (our arbitrary limit.) We know the Voltage (21.6) and the resistor value, (oh, let's say 47R) so we just solve V=IR for I. V 21.6 I = --- = ------ ~= 460 mA R 47 Now the numbers above are _completely fabricated_ so you will have to do the process yourself. The above also presumes that the measurements are taken at some fixed level of light. You will find that the numbers change with the light incident on the panel. Another point to ponder is impedance-matching. Maximum power transfer occurs when Z(source) = Z(load). Your homework for today (:-)) How does that affect the above? Watch your power dissipation. You may need to change to higher _wattage_ resistors, as the resistor values drop. 24V into 1000 Ohms gives 24 mA and 576 mW. 21.6V into 47 Ohms gives about 10 Watts ==>> heater! P = IV = .46 * 21.6 ~= 9.9 Watts Watch the resistor wattage values!
[ "What is a chip marked "TC 74HCU04P" can it be used in the MicroCore? ] Q: "What is it?" A: TC 74HCU04P TC - manufacturer's code, possibly "Toshiba" 74 - popular collection of TTL ("transistor-transistor logic") chips, most compatible in some way with others. HC - sub family of "74 TTL" Think of these as "High speed CMOS" with lower power consumption and slightly higher speed than the baseline (original) family. U - special sub-family of the "HC" sub-family of "TTL." The "U" refers to "unbuffered." Very slightly faster and greater "fan-out" than buffered version. 04 - (74xx04) "Hex inverter" (74xxU04) "Hex inverter" Q: "Can I use it in the MicroCore?" A: There are chips better suited to the MicroCore. Look for a chip with a "Schmitt" input that is able to handle slowly-varying inputs. Most TTL inputs (usually well behaved) will conduct large amounts of current in the transistion region between valid logic levels. The 74HC14 is ideal.
> >what is the difference between the fairchild's > >74act139pc-nd > & >74act139sc-nd > ??? The "ND"'s mean that you are looking in the DigiKey catalog :-) The "74ACT139" part is the number that describes the function and interface type of the chip, and they are the same. The "PC" vs. "SC", after the functional description generally indicates the type of package the chip is in. In this case (the DigiKey catalog) the information is right there on the same line of the catalog; The "PC" is a "16-dip" and the "SC" is a "SO-16". So the "PC" is for mounting through holes or into a solderless breadboard; that is the type that most of the readers of this list will be using. A few will want the "SC" version which might also be called 'surface mount' which is short form for "your hands better be steady and your eyes and soldering iron tip better be sharp 'cause these puppies are tiny."
>How does the output pin work? If I write "1" to the data port, will >the output pin go high? And if I write "0" will the pin go low? Yes, if you have the LED connected to the processor and then to the current-limiting resister and the resister is then connected to ground. BUT, If you have the resister connected to +5V and you flip the LED around, then the LED will light when a "0" is present and will turn off when a "1" is written to the port. Just be careful that the LED polarity is proper or it won't light at all! Usually, you want to sink current so the second configuration is actually better because the current will flow from the +5V through the resister and LED into the I/O pin.
How "big" is an amp and/or an mA? I mean, relative to a volt. An ampere and a milli-ampere are related at 1000:1. The "milli" prefix tells you that the following unit is to be multiplied by 10^(-3), or one one-thousandth. A volt has no [size relative to] an ampere, but they are interdependant in a circuit. For example, you will often here that a voltage of such-and-such, across so-and-so, gives rise to a current of blah-blah milli- amps. These questions suggest to me that you are ready for a beginners' electronics book. Radio Shack has one that is inexpensive, written by Forrest M. Mims III, "Getting Started in Electronics." There are some smaller and less expensive booklets there too, but start with the large one.
> What is a millAmp? milli = 1/1000th, or 0.001 of an Amp. For milliamp we write 'mA'. A mu would be for 'micro-', which is one millionth. The mu and the u are interchangeable, since they look alot alike, both stand for 'one millionth', and there isn't a mu on most keyboards.
Copyleft 1996-1998, Brian O. Bush

Brian O. Bush / bushbo@mediaone.net
Updated: Oct. 25th, 1998