The color code for a 68Ω resistor (the three colored bands on the resistor) is blue-gray-black. You can find all sorts of information about resistor color codes on the Internet, including this rather nice resistor color code converter. Another useful tool is this LED resistor calculator, which rounds the result to the closest resistance value that is actually available.
Both these tools work with, at best, 5% resistor values, the E24 range. I haven't looked at hobby distributors recently but we are finding it increasingly difficult to find 5% resistors (that were originally used to pinch some pennies), without a minimum order. It seems the technology has improved to the point where 1% reistsors are easy enough to make without sufficient rejects to justify a 5% range. It is easy enough to change the values to the E96 range- it just means tons of ECNs.
At one point, I did read that 0.1% resistors were becoming cheaper, but they were going to revert back to the E24 series rather than the E96. I am not sure where that is right now.
On a self-serving note I should mention that it is easy enough to do these calculations with any computer based tool- I have used and written about using Excel for electronics extensively. Using some variation of the LOOKUP function and a table of resistor values, it is easy enough to find the nearest standard resistor value. My latest blog on Planet Analog goes a step further and is about finding the best match for a resistor pair using standard values (as in the gain of an op-amp or the voltage of an LM317). Excel-Optimizing Resistor RatiosPart 1 and Part 2. You can see all my blogs on Excel interspersed amongst some others here.
@antedeluvian: I must say that in this day and age of word processing and electronic publishing that their data sheets are decidedly "retro" to say the very least.
They aren't alone. Some companies do a really good job at this. Others ... not so much. The datasheets from Mixed Signal Integration are distinguished as much by the useful information they leave out as by the information they actually decide to include.
For example, as David Ashton points out, from the data sheet we don't know if the spectrum values generated by the chip are linear or logarithmic. This really is a key piece of information (I'm going to determine it experimentally thsi coming weekend).
@David: I notice the minimum strobe pulse width is less (18us) than the settling time (36us) - which implies you can read the data even if the strobe has gone back high? (ie you could actually read data during the purple times in your diagram?)
David -- I decided this point was important enough that I've gone back and added some stuff to the main column (page 1) -- take a look and see what you think.
I love finding new manufacturers of speciality devices, so I looked up the manuafacturer of the MSGEQ7. They are called Mixed System Integration with some interesting devices. I will keep them in mind. They seem to have been in business for 10 years or more, but I must say that in this day and age of word processing and electronic publishing that their data sheets are decidedly "retro" to say the very least.
@mithrandir: I'll see if I can get just the front end filtering running on my Pioneer kit.
Is that a PSoC 4 Pioneer kit, or are you talking about something else?
Alas I don't seem to have many LED's with me right now
I buy bags of them at a time because I seem to use them in so many things.
Weekend project, here I come :)
Have a great time, email me to tell me how you get on (firstname.lastname@example.org and email@example.com), keep notes and take pictures -- maybe you could even write your experiments up as a column for me to post here on EETimes
My interest is piqued now. I'll see if I can get just the front end filtering running on my Pioneer kit. Alas I don't seem to have many LED's with me right now so time hunt down, scrounge or steal a few!
@mithrandir: I'm curious if you could actually push the MSGEQ7 functionality into the Arduino itself.
I'm sure you could achieve somethging like thsi in the Arduino -- I've seen software DSP versions of spectrum analyzers running on Arduinos. My problem is that this is going to be part of my BADASS Display, so I'll be using my Arduino to drive the display itself.
I'm actually running this on a chipKIT MAX32, which is more than capable of running sophisticated DSP algorithms in software -- that's the longer term plan -- it was just that when I was introduced to these MSGEQ7 chips I thought I'd give them a whirl.
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