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February 17, 2012
about 6 months ago
I bought this over three years ago and finally have a use for it! I wish at the time I had understood that common anode meant that it wouldn’t be compatible with the MAX7219 I bought with it Oh well, gives me an opportunity to use more of the ATmega pins and do it manually.
Speaking of which, Nate’s 2011 driver code seems like a great start, especially since it doesn’t require any resistors. I understand that with fast enough PWM, the LEDs are not on long enough to burn out, but is that also true for sinking or sourcing current from an ATmega pin? i.e. Does this design not require any transistors on the digit pins either? If a pin has a max rating of 40mA, won’t the digit pins be sourcing more than that, especially if they are displaying a number 8 for example? In the notes, he says that turning each digit on for 5000 microseconds will draw 15.7mA, but I don’t understand how that number is calculated. Thanks for any help!
Are these threaded? And are they larger than the ones that TOL-12033? Or put more simply, is ordering these an easy way to upgrade to larger alligator clips for the coolant-hose Third Hands? Thanks!
Tutorial - Sound Detector Hookup Guide
Thanks, Byron! For anyone reading this in the future, I replaced R7 with a 3.3K instead of 33K and replaced the 100K R8 with a straight jumper and the circuit seems to work perfectly at 5V, in both bar and dot modes. It works equally well at 9V (since I’m using a less sensitive opamp). With 9V, the input signal has a bit more range, so I adjusted R7 and R9 so the reference high voltage wouldn’t only be 3.4V. I figured it’d be nice to be able to change the sensitivity based on how loud the environment is, so I then replaced the 2.2K R9 with a 1.5K resistor, and the 3.3K R7 with a 5K POT. This lets the high voltage range from about 1.25V up to 5.4V, while keeping the LED current between 9-11mA. Seems to work well with a range of volumes.
For my breadboard test, I just created the first half of your Sound Detector (mic preamp and peak detector) using the two halves of an LM358. (I figured I don’t need the buffer opamp since the input is just going into pin 5 of the 3916, and the 358 has a wide input range). Jimbo’s 3914/3916 guide uses 5V throughout, and sets the 3916 Ref_out (pin 7) to 3.2V (using a 2.2k and 3.3K resistor, also tied to R_hi). Here you’ve connected R_hi to Ref_out through a 100K resistor (or to be less sensitive, suggested 10K or lower), but I don’t quite understand the effect of those resistors? I’m assuming pin 6 is very high impedance so what does the extra 100K do? Also, by using a 33K resistor instead of a 3.3K between Ref_adj (pin 8) and ground, doesn’t that set the Ref voltage to 20V rather than 3.4? Or is this where that 100K/10K resistor alters that? Thanks again for all the info!
I just noticed on the schematic that you designed this board. Very cool. I feel almost like I’m asking Hans Camenzind about his 555 timer. :)
Okay, so with a clean enough power supply, I’m curious about the analog LM3916 example. I have it working as you boarded it (and had done other circuits with the 3914 and 3916), but I don’t understand why the 3916 needs 13V in this case? I’ve read the datasheet as well as the SparkFun 3914/3916 guide, and I see the first datasheet example suggests 12-20V in order to support a 10V signal. But in this case, isn’t the signal only going to be about 1V? Couldn’t the 5V also supply the 3916 (even in bar mode) as long as V+ is at least 1.5V higher than the top of the input signal? Alternatively, wouldn’t the Sound Detector and LEDs work just as well with a 13V input rather than regulating it down to 5V? It looks to me like all the should support a voltage range?
I ask for practical reasons - I’d like to etch a portable version of this circuit, so I’m trying to figure out if I should power everything from a 9V battery, or maybe 4 AAA batteries, or 2 LiPo batteries, giving me a range of 6-9V. Would any of these voltages work equally well for powering both the Sound Detector circuit and the 3914 without creating two separate supplies? (I also have plenty of 7805 and 317 chips so could create the separate supplies, but I’d love to understand why its helpful.)
Thanks again for all the insight. Hopefully this will be interesting to someone else as well.
Thanks, Byron. I really appreciate the info. I’m not an engineer, but I suspect I’m pushing the limits of my inexpensive equipment ($50 multimeter and $400 oscilloscope), or perhaps the RF noise in my garage. The ExTech 330 shows 0.003V (or 3.6 mV) AC touching the leads together, although touching the leads to a 9V battery I did get the AC to drop down to 1.5mV. The Rigol DS1102 shows 4-6mV peak to peak if I connect the probe to its own ground, and 0-2mV peak to peak touching the terminals of a 9V battery. With the bandwidth filter off and the probes at 1X I get the most sensitivity, although the frequency of those noise shows up at about 100MHz, which is supposedly the speed of the oscilloscope. Touching the probe to the built-in square wave test signal it seems to be a few tens of millivots above 3V, i.e. closer to 3.1V sometimes than 3.0V, although that may just be as precise as they’ve made the test signal since its designed just to adjust the variable capacitors to get as square of a wave as possible when in 10X mode, right?
Anyway, thanks again, hopefully this setup is clean enough for using an electret mic, or that it will be when I use a 9V battery on the final version. Otherwise I’ll try using a voltage regulator to get to 9V to see if that’s cleaner. In general, are there a set of caps you recommend for cleaning up a cheap bench power supply?
I’m curious how to get such a clean power supply? You write that it should ideally read 0.000V AC and definitely be less than 10mV, which I understand given how tiny the microphone’s signal is, but I’m not sure how to get there, or if my measuring equipment is just too noisy? Using an Extech 330 multimeter in AC mode, I get 0.003V or 3.9mV with the leads not connected to anything! I get a similar reading on a DS1102E oscilloscope with the probe in 1X mode and not even connected to anything. If I attach 2 AA batteries, it still reads 3-4mV, even using the half-inch spring as a ground clip rather than the separate 4" cable. Connected to my (cheap) bench supply, I get about 6mV, which I can bring down to about 4mV if I add various capacitors in parallel. This is true from DC voltages ranging from 2V to 18V (all I tested). With the bench supply, I can see the ripple is steady at 60Hz, so I assume it’s from the mains source, but I get the same amount of noise (just not repeating) if I disconnect the leads / probes or attach them to various batteries. I assume the disconnected noise is from RF interference, but what can I do about it? Do I need to add inductors or ferrite somewhere or somehow? Thanks for any thoughts.
about 2 years ago
Sad to see this part retired! Are you guys phasing out multi-cell LiPos because they lack protection circuits? Or just getting rid of this one because the 1000mAh version is already cheap? Because of the 500 mAh’s small dimensions, I used this battery in several projects, including a strobe light in an altoids tin (http://www.instructables.com/id/MintyStrobe2-an-adjustable-strobe-light-in-an-Al/) and also on a line follower robot (instructable coming).
about 2 years ago
Urgh! I’ve had one of these for a couple years and was about to finally put it into an ATtiny project. I was testing an LM317 setup to deliver 350ma constant current but accidentally had the adjustment and output legs of the regulator flipped. So I burned out the blue LED, which is a $15 bummer. (Actually, the blue LED now glows a very feint blue when it has voltage.) For a replacement I think I’ll just a cheaper part. (It’s a good thing most electronic components are cheap, since I’ve managed to burn out several microcontrollers and various other chips.)
about 2 years ago
Have you considered carrying the 20-pin versions of these? I’ve gotten a few from EMSL but everywhere else only seems to carry the 28 and 40-pin versions. 28 is great for ATmegas, but for all the ATtiny chips, the 20-pin version seems like a better fit, especially the 2313 and 261 series.
No public wish lists :(
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