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991  Forum 2005-2010 (read only) / Interfacing / Re: Arduino + Crystalfontz Serial LCD + buttons! on: February 19, 2008, 06:45:54 am
I'm REALLY not trying to "rain on the parade".... I think the work done is great, and I've chased such things myself.... but.... for people thinking of adding an LCD display....

CrystalFontz: About $60? (for one like the one pictured in this thread)

Alternative: Serial controller, which is already working at microcontroller levels... no RS232 "stuff" to sort out, as with CrystalFontz....  $8,

To which you have to add the LCD display of your choice: Either a simple 2 lines of 20 characters and no backlight (cheap), or as big and as beautifully lit as your budget allows (within reason! You won't get 40 lines of 80 characters... I don't think...)

The alternative described in more detail at....

... and no, I don't participate in the profits. Just a happy customer. (Profits??? At $8? This is just a fellow hobbyist sharing at cost, I think.)
992  Forum 2005-2010 (read only) / Interfacing / Re: Multipe LEDs on one resistor, what values? on: March 06, 2008, 03:41:38 pm
How about this answer:

Get yourself an LED "flashlight".

Connnect it to its ordinary battery, but through a relay.

Use the Arduino to switch the relay on and off.

Any good?
993  Forum 2005-2010 (read only) / Interfacing / Interface with Dallas 1-Wire on: October 01, 2008, 08:04:54 am
The Arduino can, of course, "talk" directly to Dallas 1-Wire chips and networks of chips.

On the other hand, if you are averse to reinventing the wheel, and want to move some of the load off of your Arduino, you can use external devices.

I wrote at length about one such device. That essay's at...

Since writing that, I've become aware of another device with similar capabilites, the $18 (+p&p... $7.28 on an order of a number of things) HA7S from....

(aka the following, if you don't trust tinys...

Has anyone worked with this device? Looks like a good fit with Arduino. Comes fully assembled, you just plug it into a protoboard.  2cm x 2.5 cm, including pins, which are in the plane of the pcb. Six pins.

For those not familiar with 1-Wire....

Once you have the HA7, through it you can talk with temperature sensors, counters, ADCs, memory modules, digital I/O chips... which can be a long way from your Arduino. The chips are daisy-chained via two wires, making a "MicroLan". Each is addressable. More at...

(For those who think this post is just a self-serving bit of self promo... you are partly right. But note that all of the stuff on my pages that I refer to here is free, just things to help you enjoy your Arduino.)

Enjoy, and hoping to hear from happy HA7 users,

994  Forum 2005-2010 (read only) / Interfacing / Re: Controlling switch matrix on: February 20, 2008, 05:20:16 pm
84: Each switch has two contacts!

I thought Google was going to let me down... shock! horror! Took ages to find....

... where you'll find matrix keypads explained.
995  Forum 2005-2010 (read only) / Interfacing / Re: Controlling switch matrix on: February 20, 2008, 11:14:23 am
Are you SURE you want to take this on? It will not be easy!!! At least not taking your description of what you want to do at face value. There's probably a way to get your result, but not by the "obvious" route.

a) Do you have access to the 13 wires (6+7) by which the matrix is connected to it's host?

b) If you REALLY want to EXACTLY mimic "fingers on keys", you'll need to be able to connect 84 wires to the places on the matrix keyboard where it's SPST switch connects to the cirsuit board.

Those 84 wires could be taken to 84 opto-osolators which could be Arudino controlled, and act like "fingers on buttons".
996  Forum 2005-2010 (read only) / Interfacing / Re: Interface with PH probe on: March 01, 2008, 09:52:33 am
Sorry for the following poor reply... but better than nothing?

a) Have you decided on the pH sensor that you will be using? If so, posting the details might inspire/ enable answers. A URL to its web-home for specs, etc would be useful

b) I am no expert, but I THINK that you CAN tell op amps to shift their outputs. The demo circuits on the web are "tuned" for pH 7= 0 volts. higher = positive, lower = negative are set up that way becuase it is convenient... IF the op-amp's output is being sent to a negative-capable voltage display. But (I think) there's nothing inherent in the fundamentals of op amps to prevent you from configuring one to read 0v for pH 5, 5 v. for pH 9.

Hope this is....

1) Right!

2) Encouraging.

Sorry I can't be certain or more informative.

Oh yes. Also. Break the problem up. I suspect your pH sensor generates a very weak voltage, let's say 0 - 14 mV for pH 0-14, capable of sourcing 0.1 mA? Once you have the actual figures for your sensor, you can start looking with Google at op-amp circuits IN GENERAL... you don't need to search for an article about using an op amp with the specific voltage source you are working with.

When I've tried to work with op amps and things like the Arduino, I've stumbled on the following "What if".... "What if the op amp starts sending out a voltage outside of the range that is accepatable to my ADC? (In the case of the Arduino, outside of 0-5 volts)" Can I prevent it? Does it "matter" if I don't? (I suspect negative voltages would be a Bad Thing.

Let us know the answers when you find them!
997  Forum 2005-2010 (read only) / Interfacing / Re: Temperature Sensor on: October 03, 2008, 06:53:15 am
If -55 deg is enough for you, you'll be a lot happier with the 1-Wire chip... a joy to use. And you can have mulitple sensors easily, sometimes a consideration. And no calibrating of amplifers, etc, to contend with.

1-Wire fan club at...
998  Forum 2005-2010 (read only) / Interfacing / Re: Temperature Sensor DS18B20 and producing some heat on: October 03, 2008, 07:12:37 am
I have used DS1820s for years, with little hassle. I suspect there was something acting as a "heat capacitor" in how you had things set up. The heat sink idea is good, if you want to measure quickly changing air temperatures.... and of course, the DS1820 needs to be away from any "heat capacitor"s. You can get a smaller, SMT, chip, which is either DS1820 compatible chip or works in a very similar way, from several sources, one being DS1822Z, @$2. Beware shipping delays.
999  Forum 2005-2010 (read only) / Interfacing / Re: Arduino to power on computer on: October 03, 2008, 07:07:34 am
Excellent explanation of opto-isolators... which I agree with previous poster are things you ought to think hard about including in your circuit....

And if you want help with how the PC that DOES wake on LAN is going to "tell" the opto-isolator to tell the other one to wake up, see...
1000  Forum 2005-2010 (read only) / Interfacing / Re: Help chaging ds18b20 data in to a tempurature on: March 06, 2008, 03:38:12 pm
The web page...

... is perhaps the worst I have on the web... but in Program 2 (in that), there is actually the code for processing the data from a DS1820... if you can find it! Sorry.

The DS1820 returns two bytes.

One will either be 0 or 255 (All zeros, or all 1's)

If all zeros, your tture is above 0 deg C, and the number in the other byte is the number of half-Celsius degrees above 0 that the sensor saw. E.g., if the byte says 30, the tture is 15 degrees C; 31: 15.5 degrees, etc.

(If the one that's either 0 or 255, put the two bytes together, and you are looking at the 2's complement of the tture in half degrees. Do you REALLY want to deal with negative ttures? You CAN.. if you want to. Program 2 gives an answer.)
1001  Forum 2005-2010 (read only) / Interfacing / Re: looking for meter to interface with arduino on: April 09, 2008, 09:34:06 pm
I think the way to go would be a device that is like a motorless pump. As fuel flows through it, an impeller is turned. Each time it turns, it behaves as if someone pressed a doorbell once briefly. you feed that signal either direct to the Arduino if it isn't too busy to watch the input sufficiently continuously that it doesn't miss an on/off, or, more likely to work, feed the signal from the sensor to a counter. The Arduino then reads the counter when and as the Arduino wants.

There's more on counters at...
1002  Forum 2005-2010 (read only) / Interfacing / Re: ultrasonic range finders on: April 01, 2008, 10:30:26 am
For anyone who hasn't yet bought their range finder.....

I bought two from very reasonable shipping terms, by the way.

Ultrasonic. Really cool. Multiple outputs, but for Arduino the analog output is the easiest to use.
Measures from 6 inches to 254 (6.4 m), 1 inch resolution. (Things closer than 6 inches report as at 11 inches)

Infra red beam system.
$10  :-)
Detection range of 4" to 32". An analog voltage indicates the distance. (I haven't played with this one yet.) I'm awaiting delivery of some connectors... You can just solder wires to the device, but I thought I'd do it the "nice" way. Pololu doesn't have them. I have a few on the way. Send PM if you want one or two, $4 or GBP2, to USA or UK address.
1003  Forum 2005-2010 (read only) / Interfacing / Re: Earthmate II on: April 05, 2008, 08:20:48 am
It might be an idea to start with the Earthmate connected to the Arduino's "ordinary", buffered, serial port (pins 0 and 1). Get things working there, and then move to other pins.

Divide and conquer?

A normally-closed pushbutton switch on the data from the Earthmate to the Arduino, or even both lines, can be handy for interrupting "things" from the Earthmate coming in while your PC is uploading a new program to the Arduino.
1004  Forum 2005-2010 (read only) / Interfacing / Re: Overcurrent on IO pins on: April 06, 2008, 07:38:25 am
I HAVE blown individual outputs on a chip. Not an Arduino, specifically, admittedly, but I just thought I put my more-than-2-cents-expensive experience into this discussion.

And I'd like to underline what an earlier poster said about a "failed" pin not necessarily being obvious. It may just be degraded, and subsequent to abuse "sort of" work.

Why take the chance?
1005  Forum 2005-2010 (read only) / Interfacing / Re: Advice working with solenoids on: March 30, 2008, 04:37:20 pm
There are several things being addressed in this thread.

Do pay close attention to what people have been saying about not driving the solenoids directly.

However...the good news is that if you really only need 16, and if you don't need the analog inputs of the Arduino for anything, then those pins can ALSO be used for "normal" digital output, so you don't need to do any clever multiplexing to get the "extra" outputs.

As I said before, you DO need "extra electronics" to "fix" the power issues, though.

Someone more expert than me should also, I suspect, address the issue of a diode to "suck up" the pulse of negative voltage(?) which arises when you remove power from a coil, be it solenoid or relay.... but if someone knows the answer, could they start THAT discussion in a new thread??
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