I want to build a VU meter. I looked at the data sheet in an attempt to learn a bit about it, and I see that it has "programmable output current". if I understand this right, I can run my LED's without a resistor for each one, but I have no idea how this works. it looks like I can use the diagram on the first page. I'm going to be using Blue, Sea green and Green LED's from lsdiodes, and I want to just run them all at 3.6V and 30 mA. I'm gonna be running this off the 5V molex and connecting the input to the internal sound connector. so, the questions are: 1)can I use the diagram on page 1? 2)what values do I need R1 and R2 to be? 3)I don't need a resistor for each LED right? thanks.
Announcing the winners in reverse order, (1) You don't need a resistor on each led, R1 provides a constant current whatever leds you use. LED current = 12.5/R1 so 1k2R will give you about 10mA, (2) Make R1 1k or 1k2 to give the aforesaid 10-12mA, Don't try for 30mA, you'll just make a smell and it won't be much brighter. (3) Forget R2. Use the diagram on p6 and conect your signal across a 10k preset pot, with wiper to the signal pin 5. Then just adjust the pot so the top led lights up at maximum volume.
this one is much clearer. just 3 more quick (not really) questions. 1)do I need the 2.2 uF capacitor? I don't see it on page 5. 2)to make it bar graph, where do I connect pin 9? 3)my mobo has 8 pins for the front panel audio connector. I'll write the pins in pairs in the order they appear from left to right (it's 4 pairs) top: ANGD - bottom: MIC2 top: +5VA - bottom: MICPWR top: BLIN_OUT_R - bottom: LINE_OUT_R NC (blank space, big enough for 2 pins) top: BLIN_OUT_L - bottom: LINE_OUT_L suppose I want to conect it to the left audio channel, which of these pins do I need? and do I need to ground another one or something? thanks for the help.
1) The 2.2uF capacitor is only required if the connections from your IC to your LEDs and ground exceed 6". 2) Wire directly pin 9 to pin 3 or your V+. 3) I wouldn't know about this, maybe someone else will know - sorry. You could try connecting a speaker to any one of the two pins and try it to ground, if you get sound then those are probably the pins you will want to tap.
about that 10K POT for adjusting sensitivity, I saw on the stie I'm ordering from there's a logarithmic POT. well, if sound is logarithmic, should I get that one, or the linear one? also, what does "POT DUAL 10KOHM LOG. PCB/PANEL" mean? if it's like those 6 leg on-off-on switches that I can control 2 circuits without them merging, it would be great cause I'm making one for each audio channel, and this way I can make them both the same sensitivity.
I was thinking in terms of preset pots, which are all linear. Depending on the soundcard output, you may need to set volume at maximum in software to get enough voltage from line_out to light the full bargraph, all depends on the specs. The basic circuit needs 1.2V for the top led to light, though you can make it more sensitive if necessary. RTBM, us guessing is pointless when you've got the facts to hand.
what's a preset POT? quite a newB here. and I read the manual, it's not there, I triple checked. all it says is that by default the pins "LINE_OUT_R\BLINE_OUT_R" and "LINE_OUT_L\BLINE_OUT_L" are shorted with jumper caps. will using a multimeter cause any problems?
They mount on the circuit board and are adjusted with a small screwdriver - set & forget. Picture here. I think the line_out pins that are linked are across a break in the line_out track to the line_out jack socket, so one pin will connect straight to the jack, the other will carry the signal from the source. You'll still need to keep them jumpered if you tap your vu-meter signal from that point or you'll lose the jack signal. Basically you've one of two ways to go; (1) If the line_out signal is over 1.2V you'll need a pot across the output (3915 input) to cut the signal down, (2) If the line_out signal is under 1.2V you'll need to either boost the signal with an op-amp or increase the meter sensitivity. To do that you make R1 a 1k pot taking the wiper to pin 6 on the 3915.
unfortunately there is only one big online electronics shop in israel, and it's got a crappy search function, and it's partially hebrew. it doesn't support multiple words, it's treats them as one string. I searched for "preset" and "cermet" but no results came up. when I searched for 10KOhm it brought up lots of resistors, but also a few POT's and a few "trimmers" which I have no idea what they are. if those aren't what I need I'll just get normal ones and find a place to put them.
I searched the junkyard that is my room and found what looks like it once had an LED/reset switch on it's end but it was cut off. 2 wires with that end connector that looks like a jumper. I connected this to the "LINE_OUT_R\BLINE_OUT_R" pins instead of the jumper, and connected the wires to the multimeter. there was no reading, but the right audio channel didn't work unless I made the wires touch. does this mean one of them is what I connect my signal to and the other is ground? how do I know which is which? and how do I connect my circuit to them without muting my headphones? unless I risk damaging the mobo (which I doubt), I think I can just connect the circuit to the wires I used for the test, see if it works, and if it doesn't I'll connect it upside down. thing is, I got no idea how. you said to connect the signal through a 10K POT to pin 5. what about the other pin on the mobo?
That suggests it's as I thought above, just a break in the signal track so you can connect in a front panel volume control. Leave the two jumpered and take your signal from the jumper and a ground to each end of the pot. Might be better with 100k pot instead of 10k, less drain on the speaker amplifier input.
