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331  Forum 2005-2010 (read only) / Interfacing / Re: Looking for Bluetooth Module on: November 20, 2010, 07:57:51 pm
Just came across this, which is class 2:

or this which is class 1:
332  Forum 2005-2010 (read only) / Interfacing / Looking for Bluetooth Module on: November 20, 2010, 07:11:24 pm

I am just looking for a bluetooth module for my project. I dont want an Arduino shield, but a module which I would plug into a custom PCB, or solder directly to it etc. (Similar to a WIZ812MJ type module)

It needs to be compatible with an Arduino (not using an arduino board, but a custom board with a 1284P on it).
It can either communicate over UART, SPI or even I2C.
It needs to be able to have an external aerial connect to it, rather than a built in one only.

I am trauling the forum looking but havent found one yet. Anyone know of anything?

333  Forum 2005-2010 (read only) / Interfacing / Re: Digital Pot - 3 joined to double resolution on: November 15, 2010, 01:07:19 pm
Thanks Mike, good info there.

Thanks CrossRoads - I will have a good look at that site, could be useful. That smt video site sounds great too.

334  Forum 2005-2010 (read only) / Interfacing / Digital Pot - 3 joined to double resolution on: November 15, 2010, 03:20:15 am

I have been doing some reading about the AD5171 (i2c 6bit digital pot) chips, and in the datasheet it states the following ( page 20:

The resolution can be doubled in the potentiometer mode of operation by using three digital potentiometers. Borrowed from ADI's patented RDAC segmentation technique, users can con-figure three AD5171s (Figure 46) to double the resolution. First, U3 must be parallel with a discrete resistor, RP, which is chosen to be equal to a step resistance (RP = RAB/64). Adjusting U1 and U2 together forms the coarse 6-bit adjustment, and adjusting U3 alone forms the finer 6-bit adjustment. As a result, the effective resolution becomes 12-bit.

That sounds great, but the chips are only available in small SMT packages, and I really want to prototype with DIP. There are various SPI chips in DIP format that are cheap, and I was wondering if anyone sees anything wrong with putting 3 of these as described in the AD5171 description, in order to get a higher resolution?

335  Forum 2005-2010 (read only) / Interfacing / Re: 7 Segment Display - Common Anode on: November 13, 2010, 09:44:34 pm
Thanks Guys

Hi Rob smiley - This is in parallel with the conversation we had offline smiley

Its good to see my question has been understood.
CrossRoads - yes you have it bang on, that is what I want to achieve.

I was talking to Rob (Graynomad) offline, and the question came up about multiplexing and what effect that has on the brightness of LED's like this. Basically if I have 4 displays in parallel, switching between them really fast, they effectively have a duty cycle of 25% - correct?
How does that effect the brightness, compared to powering the displays individually.

As Rob pointed out, the headroom is slim - 11.6V to 12.4V. If they are multiplexed, effectively PWMing the 12V source, will the voltage have to be boosted in order to keep the average within the required limits, to then keep the display at full brightness?

This is just one of the problems. 12 wires for 4 displays is the aim, but will a simple 12V source be sufficient, or will it required a variable regulator or something in order to ensure the displays are full brightness?

RE the MAXIM 8 digit driver, that is what I used first off. But since its common cathode designed, I had to use transistors (or FETS) obviously, plus the fact they require 12V. Transistors caused the voltage drop which dimmed the digits which I want to get around and FET's would fix this. I then thought about just using an IO expander or a 2nd processor and just powering each individually. That made the 36 wire solution though. The final version I want to fit in the same footprint as other baords I have made, which means I can only fit 12 wires.

All good solutions but a number of questions too.

336  Forum 2005-2010 (read only) / Interfacing / Re: 7 Segment Display - Common Anode on: November 13, 2010, 08:22:05 pm
To make things clearer, basically the driver board I want to make, assume its a shield for the Arduino. The 7 segment displays are mounted a few meters away.

I am not using arduino hardware for this project, still using the Arduino IDE for programming etc, but not a production arduino, but the concept is the same.
337  Forum 2005-2010 (read only) / Interfacing / Re: 7 Segment Display - Common Anode on: November 13, 2010, 06:47:49 pm
Very basic diagram to illustrate.

Note, blue wires on the right hand side are common to each of the 4 displays, even though they are only shown to the first one.
Hence, 12 wires total OUT OF the driver board (which I want to make) to the 7 segment displays.

I hope this is clearer, but it is what I have been stating above.

338  Forum 2005-2010 (read only) / Interfacing / Re: 7 Segment Display - Common Anode on: November 13, 2010, 06:32:13 pm
You are talking about the input wires from the arduino to the driver. I am talking about the output of the driver to the 7 segment digits.

The 7 segment digits have 9 wires on them each (8 cathodes, 1 anode).

You are not talking about the same wires as I am. I dont care about the arduino to driver wire requirement. I only care about the output of the driver to the digits.
339  Forum 2005-2010 (read only) / Interfacing / Re: 7 Segment Display - Common Anode on: November 13, 2010, 06:06:56 pm
That is fine but it doesnt fit the requirements I have for this project!

I can only have 12 wires coming off this board to the 4 digits. I dont know how many more times I can say that.

Your solution requires 9 wires for each digit. I dont have room for that on my board.
I have a predetermined wire to PCB header on the PCB which only has room for 12 wires. The only solution I can think of is 8 common, 4 digit selects.
I am trying to build a driver which suits this requirement.

most simple, straightforward, easiest, and cheapest way
- thats fine, but that is not my requirement!
Its like im trying to build a car here, and you keep telling me to walk because its cheaper.

I already have a solution which can drive 4 digits with 36 wires. I want to drive 4 digits with 12 wires. This is the whole purpose of this post. To find a solution which can achieve this, to drive 4 digits at 12V common anode using 12 wires.
340  Forum 2005-2010 (read only) / Interfacing / Re: 7 Segment Display - Common Anode on: November 13, 2010, 05:57:24 pm

GND, +12V and I2C out to the display...?
The display doesnt take i2c... its just a 7 segment display.

I am trying to build the driver here

An example of what I almost want is on this datasheet. Page 12.
The only exception is, this driver is only capable of driving 2 digits off common wires, which isnt quite good enough for what I need. This diagram shows 8 wires which are common for 2 digits, and 2 digit select outputs. This means there are 18 wires required to drive 4 digits, which is still too many. I need 8 wires common for 4 digits, and 4 digit select outputs.

Am I not explaining this well enough?
341  Forum 2005-2010 (read only) / Interfacing / Re: 7 Segment Display - Common Anode on: November 13, 2010, 05:45:54 pm
The 12 wires, as mentioned above are just the 4 digits segment LED's in parallel with each other, with seperate digit select wires each.

ie digit1 has 8 wires for the segments and the decimal point. These are in parallel with the other 3 digits. The anode supplying 12V to the digits are seperate for each digit.
So that is 8 wires that are common (7 segments + decimal) and 4 wires that are seperate (12V feed to each digit).

Those are the requirements I have. All the rest is fully open to suggestion. i2C, SPI, parallel, etc.

All I want to know if anyone has a known combination that works to drive these displays, with the outputs the are basically multiplexed so there are only 12 wires maximum out of the driving circuit to the 4 digits.

I have read over my lasts posts and I explained this in my first post. Im not sure what there is further not to understand.

I have on breadboard a driver which each digit has its own wires, but that is a total of 36 wires to feed the 4 digits, as none of them are common.
I want to find a solution where I can parallel up the digits and have a digit select - but suitable to drive a common anode display at 12V.
342  Forum 2005-2010 (read only) / Interfacing / Re: 7 Segment Display - Common Anode on: November 13, 2010, 05:30:13 pm
So no ideas then...

Righto - thanks.
343  Forum 2005-2010 (read only) / Interfacing / Re: 7 Segment Display - Common Anode on: November 13, 2010, 05:06:26 pm
12 wires, as in the output of the circuit which goes to the 7 segment displays. Not 12 wires to go into this driver circuit like you think I mean.

Whatever goes between the arduino and this driver circuit doesnt really matter. Its the output of the driver circuit TO the 4x 7 segment displays can only be 12 wires.

344  Forum 2005-2010 (read only) / Interfacing / Re: 7 Segment Display - Common Anode on: November 13, 2010, 04:34:45 pm
Thanks - I had seen them, but from what I can tell, you need one of these chips for each of the digits? ie to control 4 digits I would need 4 chips, and therefore 8 or so wires going to each digit...?

I can only have 12 wires total going to all 4 digits.

I may have misinterpreted what I quickly just read now though.

I just found another site.

I havent read it fully yet, but it uses another chip to drive common anode displays.

And yes, the price on sparkfun is not cheap - luckily I didnt get mine from there but its just easy to link to their stuff smiley-razz

345  Forum 2005-2010 (read only) / Interfacing / 7 Segment Display - Common Anode on: November 13, 2010, 04:14:41 pm

I was just wondering if anyone has an idea for the best way to drive 4x large 7 segment displays that are common anode (which is not the norm) that each require 12V forward voltage to run.

The displays in question are here:


It has been mentioned on here before, however there were no shared outputs between the displays which I am requiring due to the PCB footprint this driver board will be going on to.

Basically I want the arduino to either output I2C, SPI or digitial outputs to a chip which can then drive 4 of these displays. Basically a shift register or multiplexor, but to drive common anode.

I want 12 wires coming out. The 7 segments and the decimal point, which would be common wires between all 4 displays, and then 4 select outputs to chose the display to update.

I have looked at the 74HC595 shift register and thought about putting a darlington array after it or something - but is this the best way?

The displays take 12V (from 11.6v to 12.4v), so with a supply of 12v going through the darlington arrays, you get a voltage drop which would dim the displays (as I have tested). I could use FET's I suppose, but is there another solution?

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