Hello fellows,
I am a newbie electronic hobbyist. I am currently working on one arduino spl project. I need to connect an spl meter to an arduino and control a servo motor based on sound pressure detected by spl meter. First I was planning to create an spl meter using arduino but the spl meter that i created was not fast and accurate, since I didnt have much time to work on it I decided to buy a separate, cheap SPL meter and connect it to my arduino. However, I have never done any hardware hacking before, and since there is NO schematics for digital spl meter (specially the model that i own ) I have NO CLUE where is the SPL meter's out put. I have stared hours on circuit tring to find out how I can connect my SPL meter to arduino. my initial though was maybe there is a data LCD pin that can help me. but I was wrong! I have uploaded the SPL board pictures too. It is Hobbyking Digital Sound Level (dB) Meter.
ANY IDEA? SUGGESTION?
ALSO, out of curiosity, meter's LCD is really weird to me. there is no pins on LCD, do you know what kind of LDC is that? (pictures uploaded). It is like a glass attached to the board through a plastic, but there is no pins on it!
Somewhere on the board there is probably a DC voltage that varies with loudness. If you "probe around" should be able to find it. There may be more than one variable-DC voltage on the board, so don't stop when you find the 1st one.
I'd start by probing the IC pins. I couldn't identify the ICs on board, but if can identify one (or more) as an op-amp (operational amplifier) an op-amp output-pin is a good place to start probing.
If you don't have a multimeter, and LED with a 1k resistor in series might work (the brighter the LED, the higher the voltage). However, the LED won't come-on 'till you get about 2V so you might not find the connection. And, the LED won't tell you if you are exceeding 5V which could damage the Arduino.
You can also use the Arduino as a voltmeter/probe. If you are not sure about the voltage you are connecting to the Arduino, use [u]protection diodes[/u].
It's likely impossible to "decode" the digital data going to the LCD. It could be a matrix connection, serial or parallel, and you don't know what the protocol is or what pins are what...
Somewhere on the board there is probably a DC voltage that varies with loudness. If you "probe around" should be able to find it. There may be more than one variable-DC voltage on the board, so don't stop when you find the 1st one.
I'd start by probing the IC pins. I couldn't identify the ICs on board, but if can identify one (or more) as an op-amp (operational amplifier) an op-amp output-pin is a good place to start probing.
If you don't have a multimeter, and LED with a 1k resistor in series might work (the brighter the LED, the higher the voltage). However, the LED won't come-on 'till you get about 2V so you might not find the connection. And, the LED won't tell you if you are exceeding 5V which could damage the Arduino.
You can also use the Arduino as a voltmeter/probe. If you are not sure about the voltage you are connecting to the Arduino, use [u]protection diodes[/u].
It's likely impossible to "decode" the digital data going to the LCD. It could be a matrix connection, serial or parallel, and you don't know what the protocol is or what pins are what...
Thanks DVDdoug,
I checked out the circuit. I do have multimeter. there are 6 chips on it. 3 op amp, one MUX and one charge pump voltage inverter. I check out out output pins on opamps and one one them close to microphone was kind fluctuating based on noise level that microphone receiving, however it was fluctuating really wild. I am going to see how arduino will respond to that.
meter's LCD is really weird to me. there is no pins on LCD, do you know what kind of LDC is that? (pictures uploaded). It is like a glass attached to the board through a plastic, but there is no pins on it!
A bit late, but some general info on the LCD: This is a very simple LCD, just the glass, plarising film, electrodes, liquid crystal material and sealing/spacing. LCDs have transparent conductive coatings in the shape of the segments on the glass, and for simple LCDs the opposite side is a continuous backplane. The liquid crystal material is trapped in a thin layer between these electrodes, and with no voltage applied the needle shaped crytals align to a keying layer on each glass aligned with the polariser, twisted 90 degrees across the layers. Light entering the display is polarised, then the plane of polarisation is twisted passing through the liqid, then passes through the second polariser. If voltage is applied between the backplane and segment, the crystals align with the electric field, so don't twist the light polarisation, so don't alow light through. The 'plastic' is an elastomeric connector, a rubbery strip with conductive strips so there is connection from the PCB to the LCD glass, but not along the length, so the strip doesn't have to be as precisely positioned - only the glass to PCB. I suspect that if you examine the plastic through a magnifier, you will see it is a stack of black (carbon loaded) conductive plastic layers alternating with non-conductive (often clear), this alternating structure gives the normal name of 'zebra stripe' for this type of connector. Some similar LCDs have pins crimped to the edge of the glass at to make the connections instead of using a zebra-stripe connector. All segments and the backplane are driven with a (0 & Vcc) square wave; if the segment square wave is in phase with the backplane the segment is off, if out of phase the segment is on (about 30-250Hz, cheap older equipment used DC for on, 0V for off but this degraded the LCD - the net result of using in-phase and out-of-phase is no DC bias in order to avoid this problem). If the display is a complex (e.g., graphics) one there may be multiple backplanes and the segments and backplanes will be driven by narrow pulses going both above and below an intermediate voltage; if the display has greyscale, then those pulses will be of varying voltage; colour displays are just greyscale with RGB filters carefully aligned; most displays more complex than simple graphics will have the driver chip bonded to the glass. If it is a simple display (it looks like it) you could try capturing enough segments to decode the digits, but you'd have to identify the backplane and segments, and you have to get a consistent capture (capture twice then keep capturing until you get two the same, so you've got to capture 40-odd lines and do the compare in 1ms or better). Try looking up the number of the chip which is most connected to the display, it may be an SPI or I2C LCD segment driver chip in which case you have a decent chance of capturing the data, but if the equipment has been cost-optimised the segments may be driven direct from micro outputs if there are enough of them.
Should have looked at the pictures of the PCB first - with only 13 connections, this has to be a display with chip-on-glass display connected by the zebra-stripe through to the micro under the epoxy blob. Careful probing with an ocilloscope should reveal the data connection pins, but that's only a small part of the problem.
