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1  Forum 2005-2010 (read only) / Interfacing / Re: Arduino +Sparkfuns 4-digit 7-segment 16pin display on: March 02, 2010, 12:26:48 pm
I picked up one of those (the blue ones) and i'm looking for a driver for it.  I can't seem to find any decent digit multiplexing ICs for a CA display.

SAA1064 does pretty much everything I want it to (I2C, self multiplexing, small programing footprint, little processor overhead) but I don't figure I can get it working with that display (at least not for 4 unique digits).

I don't want to go with a BCD unless it'll output Hex as well (can't remember the proper name for them).

I figured out a decient solution using 4x 8 bit shift registers, a 4 bit (or and multiple of 4) an 8 channel mux, a few transistors and an oscillator.

Thus far, octopart has failed me in my search for a 7-segment 4 digit(+) driver w/ CA. Can I just use a chip made for CC and use some transistors?
2  Forum 2005-2010 (read only) / Interfacing / Re: ICM7218A on: March 28, 2010, 01:22:52 pm
Okay, so I got a circuit designed for this chip, and I want to make sure that I'm not going to blow up my LEDs.

I'm working with 2 different colors, each with a different forward voltage and maximum current.

The datasheet for the ICM7218 says...

VDD = 5V, VSS = 0V, TA = +25°C, Display Diode Drop = 1.7V
Digit drive current: Common Anode VOUT = VDD -2.0V 140-200mA

The yellow 7-segment says...
The LEDs have a forward voltage of 2.1VDC and a max forward current of 20mA

would I then calculate the resistor as Vout - Forward Voltage * A?
(3-2.1)/0.20=R or 45ohm+ resistor per segment?

The Blue LEDs have a forward voltage 3.4V. Can I run these without some way of increasing voltage of the segment output?

I know these are some seriously noob questions, thanks for all the help!
3  Forum 2005-2010 (read only) / Interfacing / Re: ICM7218A on: March 08, 2010, 03:43:34 pm
Oh okay, I think I get how it works now.

Even requiring as many pins as it does, if I send only Hex/Code B I think I can run it off of 6 pins, much much less than the 12-16 that would be needed for 4/8 digits.
4  Forum 2005-2010 (read only) / Interfacing / Re: ICM7218A on: March 07, 2010, 12:17:07 pm
The lCM7218A and 1CM7218B feature two control lines
(WRITE and MODE) which write either 4 bits of control
HEXA/CODE B) or 8 bits of display input data. Display data
is automatically sequenced into the 8-byte internal memory
on successive positive going WRITE pulses. Data may be
displayed either directly or decoded in Hexadecimal or Code
B formats.

That doesn't allow for 2 wire control?
5  Forum 2005-2010 (read only) / Interfacing / ICM7218A on: March 06, 2010, 01:52:47 pm
I'm reading over the datasheet for ICM7218A ( I can't seem to see the purpose of ID0-ID7. It looks like those lines are used for ICM7218C/D for parallel write, while A/B uses MODE and WRITE for serial communication. I can't seem to figure out why they show those pins in the schematic. am I reading this right?

Thanks in advance for the help.
6  Forum 2005-2010 (read only) / Interfacing / Re: What is the best way to control 6 seven-segments? on: April 19, 2010, 12:21:30 pm
There are tons of driver ICs for either CA or CC 7-segment displays. I've found CC to be a bit more common, but either way there are plenty that will allow you to drive 4 or more digits off of 2-4 pins.

Check out ICM7418, there are 2 versions of both the CA and CC version, and can be run off as few as 6 pins for 8 digits (BCD/Code-B only) and does all the plexing for you. At most, it takes 10 pins and can write to each segment individually (a/b) or can address which digit to update (c/d).

There are quite a few I2C chips out there, as well as other interfaces.

If you have the extra shift registers, you can always just daisy chain 6 of them and leave them on for full duty cycle (assuming that you have individual digits and not shared segments between digits).
7  Forum 2005-2010 (read only) / Interfacing / Re: advice on hardware needed... on: April 05, 2010, 02:29:22 pm
Would making an IR beam work?

If you are able to have the 'object' fall between 2 points in space (through a IR line, between a reflector and an emitter) and only that object will go through that area, you should be set.

If you need to identify objects, or discern which ones will cause a trigger and which wont, much more logic or hardware will be required.

If you can explain better as to what you want to happen and the physical constraints, your answer quality will improve drastically. Oh, and drawings help too.
8  Forum 2005-2010 (read only) / Interfacing / Relay Help: Latching relay w/o power failure = off on: April 05, 2010, 03:07:47 pm
Basic premise: I have 7 free pins (A0-5 + D8) and am looking to run 4 or more relay circuits (110v AC, 10-30A) and 6-12 sensors. I also have some 74HC595's run up on a buss, and have one free pin on that buss for adding in another one. It would take one additional pin per additional 74HC595, and programming may become more complex.

I could run a Shift Register for my relay circuits, but that would limit the number of relays to either 4 and a mux chip for sensors, or all 8 and chewing up extra pins for muxing sensors.

I was thinking of using the shift register with 2 16 channel mux chips, one for relays and one for sensors. Problem with muxing is keeping multiple relays open concurrently. I wouldn't mind a latching relay, but I want the circuit to default off on a power fail condition.

I was thinking of using 3 relays, 2 NO and a NC, one of the NO being the load (VAC) relay. My idea is putting the 2 relays (NO & NC) in series feeding into the load Relay, with the current back-fed into the coil of the NO switch. Would this give me the ability of turning on the load from powering up the NO coil but keeping it on until I juice up the NC coil? See pic below, pretend the LED is my Load Relay.

Would it be possible to toss in a diode on each of the coils so I could turn it off/on from source/sinking current from a single pin? Could the same thing be done easier (cheaper) using a MOSFET and a JFET? Is there a relay type out there that does what I want and I just can't find them?

9  Forum 2005-2010 (read only) / Interfacing / Re: 7 segment display, 12 digit multiplexing on: April 02, 2010, 10:34:16 am
I'd tend not to use emitter followers like this - the voltage drop across them might be too high to drive 3.4V LEDs and the power dissipation will be shared between resistor and transistor in a manner too dependent on the transistor gain.  Prefer to use a common-emitter drive (remember this will invert the sense of the output).

For driving the digits common anodes, use PNP, connect shift-register output to base via resistor, emitter to Vcc, collector to the digit's common anode.  Arduino pins can drive 20mA direct so they can go to the multiplexed segments so long as you only drive one digit at a time.  Multiplexing the segments is easy to code since a byte contains 7 segment bits and a decimal point bit, simple lookup table will work.

If the total digit current is 160mA and transistor has beta >= 100, then 2k2 base resistor should work, play safe with one a bit lower to ensure saturation...

Do you have any suggested reading so I can understand what you said?

Are you saying to swap around my transistors (PNP on Anode, NPN on Cathode)?

Just to make sure that I'm thinking about this right:
On a common anode display, the digit pin is the anode, and each of the segments are the cathodes. Assuming I am only running one digit, max current for the anode is 160mA and each segment is 20mA?

If you're talking about three 4-digit displays, you might consider a modular approach --> three individual 4-digit display modules on a 5-pin buss.

If I am reading this correct, you are suggesting to tie each digit to the corresponding digit on the other displays and using a shift register for each display?

If I'm reading this right, tying SER and SCK to digit pins, you're dumping data into the shift register but not latching it into the storage. During data transfer to the registers, OE goes high keeping the display blank while loading data off the digit lines.

What happens when PWM OE for dimming? is port manipulation/PWM fast enough that RCK doesn't trigger? Do I just have to keep the PWM pulses under 20ish ns to keep it from tripping? isn't 1 clock cycle (@ 16MHz) like 600 something ns?
10  Forum 2005-2010 (read only) / Interfacing / 7 segment display, 12 digit multiplexing on: April 01, 2010, 09:13:43 pm
I am trying to draw up a schematic for running 3x 4 digit 7 segment CA displays. I think I've got this right, but would like to make sure I am on the correct thought train.

First, for the segment specs:
Forward Voltage: 2.1 or 3.4 V
Max forward current: 20uA

I haven't yet decided if I'm going to plex the digits or the segments. I would prefer to plex the segments to keep a flicker down, but it seems more realistic to plex the digits with a multiplex chip or shift register on the segments. I suppose I could daisy chain 2 registers for the digits, but that seems excessive.

Is the below correct?

Plexing Either:
Source pin to NPN Base
Vcc to NPN Collector
Digit Anode to NPN Emitter

Sink pin to PNP Base
Segment Cathode to PNP Emitter
GND to PNP Collector

Minimum Resistor @ 2.1 Forward Volts: 145 Ohm (5-2.1) / .02
Minimum Resistor @ 3.4 Forward Volts: 80 Ohm (5-3.4) / 0.02

Plexing Digits (Turning on one digit at a time):
Source/Drain current Max: 160mA (20mA/segment * smiley-cool
1 Resistor per segment

Plexing Segments (Turning on one segment at a time):
Source/Drain current Max: 240mA (20mA/digit * 12)
1 Resistor per digit

As an offshoot question, can I emulate PWM by port manipulation? If I can, how will that work with a transistor either sourcing or sinking current?
11  Forum 2005-2010 (read only) / Interfacing / Re: Two seven segment displays on: April 01, 2010, 08:32:26 am
If you are using individual digit displays (or 2 digit displays) check out SAA1064. It'll do 4 7 segment (to pairs of 2 multiplexed) with an I2C interface. Chip runs about $2-3.

I went with ICM7218A due to having 4 digit 7-segment displays. It's not I2C (so it uses more pins, or a shift register) but it will run 8 digits in any package configuration (assuming segments are multiplexed).

If you're going to skip the chip, the number of pins used will be (No. of Segments) + (No. of Digits). Once (No. of digits) > (No. of Segments) it makes more sense to plex the digits rather than the segments.

By mixing CA and CC displays, I suppose you could charliplex them, further reducing your pins required, but I sure couldn't tell you how to wire something like that up.
12  Forum 2005-2010 (read only) / Interfacing / 7-segment 4-digit CA display on: February 15, 2010, 10:19:00 pm
I picked up a 7-segment 4-digit CA display from sparkfun. I'm looking to offload my display to some sort of IC (preferably TWI). Also, I would like to be able to control each of the segments independently (looking for some custom characters). MAX69xx looks promising, although the DS says it's for CC. SAA1064 looks fantastic but it won't run 4 digits multiplexed together (2 2digit segments).

Am I stuck running this directly from the processor (or sub processor even) or just ponying up and getting a new display?
13  Forum 2005-2010 (read only) / Frequently-Asked Questions / What does "I(subscript)F" mean? on: April 09, 2010, 08:52:36 am
I'm reading over a datasheet for some LEDs and in the forward voltage section it lists...


What does this mean? Effective current (Ieff)?
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