Calling audio electronics people: LM3914 bargraph IC

[Eric The Viking]

I want to make some small audio "meters", just to indicate signal present, signal "roughly right", and signal over (three LEDs). I need a pair in a bit of portable kit to connect to the audio inputs of a cheap camera (with limited functionality). there is a vague woodwork connection, honest!

I've been looking at the TI (and others) bargraph LED driver LM3914. It looks perfect for the task (3V power rail, simple enough for me to understand(!)), but I only want to drive 3 LEDs not 10, picking the LED outputs I need to give the necessary range.

I don't think three LEDs will be a problem, but as the chip seems to be fairly common, I wondered if anyone else has used it and can comment... and if it's a poor choice, then what?

E.

PS: The intent is that the IC won't be on all the time, just used for level-setting and then turned off, to preserve battery life. Thus I'm not worried about 'clever' LED drivers that pulse them.

 

[Woody2Shoes]

I used a couple of these over 35 years ago (!!) they were just fine. I'm sure you can use them with just 3 LEDs if you want to - they're funner with more though.

You could also just use transistors of course - esp. with only three LEDs! Cheers, W2S

 

[Eric The Viking]

I used a couple of these over 35 years ago (!!) they were just fine. I'm sure you can use them with just 3 LEDs if you want to - they're funner with more though.

You could also just use transistors of course - esp. with only three LEDs! Cheers, W2S

Quite agree on the more-is-better thing, but it needs to be simple - to read, and for muggins here to make!

Display: nowt, 2-small, OK, 2-much

Experience tells me this will do the job (if I pick the right values), and I need it to be easily calibrated. I'm thinking about the LM3916 [edit: LM3915 as it's cheaper and I don't need proper ref. level calibration] actually as it's log and covers 26dB - ideal for my application. (the LM3914 is linear (didn't realise until just now).

 

[Gerry]

If you have any inclination to program things then have a look at an Arduino.
You will be able to drive whatever number of leds you require and feed the analogue audio input directly in to the board

Gerry

 

[Eric The Viking]

If you have any inclination to program things then have a look at an Arduino.
You will be able to drive whatever number of leds you require and feed the analogue audio input directly in to the board

Thanks, but it all has to fit into the smallest possible diecast box and still have room for PP3s etc. I'm even struggling with long DIP packages, TBH. I don't think I have room for 10-LED meters either. It's for a "professional" interface to a video-recording SLR, and will either clamp to a tripod leg or fit on a bracket under the camera, so size is important.

I'm doing one for me and one for a friend, and unfortunately, as we have different brands of camera both will be prototypes. The main reasons are to use the best possible connectors away from the tiny, easily-broken ones on the camera itself, and the need to feed different things to the two audio channels with up to 50dB difference in incoming level (hence some gain + pads + metering).

I oscillate between being amazed and annoyed by what modern cameras can do (for the money). I have a Canon 6D, and am experimenting with Magic Lantern, which is brilliant in so many ways, but also frustrating, as it doesn't (yet) support the very limited audio features on my own Canon. There are some parallels with the Arduino world though, as it's a wonderful example of what can be achieved by open-source collaboration. There is some hacked firmware for Panasonic (my friend's choice), but there doesn't seem to be the same sort of supported API so it's not so clever.

The neatest audio trick I've seen in Magic Lantern is supporting balanced mics by phase reversing the right channel of the mic inputs, summing both and sending the resulting mono signal to one "track" of the camera (internal mic sent to #2). Elegant solution to an annoying problem, but frustratingly, unavailable on my camera presently (I fear it'll be a hardware limitation).

Thanks for the thought though.

E.

PS: Magic Lantern is actually a firmware extension rather than an application, analogous to the BIOS extensions sometimes loaded by PC cards (video, mass storage controllers, etc.).

 

[novocaine]

I'd have to agree with the arduino idea, get an ardunio nano or mini, they are tiny. if thats still to big, prototype on the board then use the IC and a selection of components to make your own tiny tiny piece of kit. anything you do analogue will be bigger than using an arduino.

 

[Eric The Viking]

I'd have to agree with the arduino idea, get an ardunio nano or mini, they are tiny. if thats still to big, prototype on the board then use the IC and a selection of components to make your own tiny tiny piece of kit. anything you do analogue will be bigger than using an arduino.

Thanks, but after a happy accident in a DSLR forum this morning, I think I'm about to drag myself into C21st (kicking & screaming). I've just seen these:

(It's a Tascam DR-70D).

4-channel recorder/mixer, even with limiters and phantom power (24V & 48V). Runs off AA batteries. Not big (judging by that XLR on the side). fits nicely under an SLR.

On the Bay around 180 quid (reputable UK seller, apparently).

For that, Maplin* can keep their diecast boxes!

I will make up my own leads though, it's a matter of principle...

E.

*Wouldn't dream of actually buying components from them these days - can't afford a second mortgage.