[possible]

I see no reason you can't tie Rx and Tx together on the chip. Of course it will require some fancy foot work to turn around the Tx pin so the two devices don't clash.

It's possible you can't use the Serial.print etc functions, although you probably can if you wrap the transmit in the pin swap code

Code:

pinMode(txpin, OUTPUT);
Serial2.print ("xx");
pinMode(txpin, INPUT);

Sort of thing.

I know we had a similar thread about some time ago (although with software serial) and this worked.
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Rob

Doh, of course it will. I should have seen that.

Any ideas how I could resolve this?

Yep, use shift registers.  

OR a 16-seg driver like the MAX6954, supposedly available in a DIP 40 but I can't find any.

Then there's the ICM7244

http://search.digikey.com/scripts/DkSearch/dksus.dll?lang=en&site=US&WT.z_homepage_link=hp_go_button&KeyWords=icm7244&x=23&y=20

SMD only though.

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Rob

That looks about right. Let us know if it works.

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Rob

[never]

I haven't looked at the 7219 specs properly but I assume it pulls the digit select low as they are common cathode.

In that case you want say digit 1 and 2 to activate the same display. So the logic is

OP low if IP1 low OR IP2 low

That's an OR function with inversions on all pins, aka an AND function.

That's working on the digit being driven from a single 7219.

either one or the other MAX driving that line but never both

I can see no way of connecting both chips to a single display, they would never be synchronised and segments would be lighting up all over the place.

2 MAX would drive the same common cathode at the same time. Do you think that makes no sense?

Yes I think that makes no sense , because of the above reasoning.

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Rob

Those diodes are what I was suggesting, they form an AND gate (XOR is not the right logic function here).

However I don't see the need for the second 7219, you have the equivalent of 4 digits and that be handled by a single chip.

Also you don't have the segments in parallal, eg A1 goes to G1. That will make your code really difficult as the bit pattern for a given character will be different for each display.

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Rob

only have a single common cathode. So I can't connect 2 of these to one digit.

Just a little thinking outside the box, can you AND two digit selects together.

74595s aren't really designed to drive LEDs, they will need driver chips and resistors.

Have a look at TLC5926 and TLC5927, 16 channels and constant current so only a single resistor to set current.

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Rob

The ATtiny85 is my weapon of choice for simple circuits, technically it's an overkill but at $3 and a bit of programming why not?

The only catch here is that it will need a regulator as well, so the circuit gets a little more busy. On the other hand because it's a processor you can add features later when you think of them.

Another advantage to using a processor is that you can easily control a latching relay, this means that almost NO current is being drawn for 23hrs 59min 59.8secs of the day. You just need an ON and an OFF pulse each day. As opposed to a normal relay that will consume power all night (or day depending on how you wire it up).

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Rob

+ and - for load (light)

Either hook your on/off circuit to these or directly to the battery, it makes no difference except using the regulator load OP will protect the battery should it ever get too low.

For the cost of an ATtiny85 I'd bung one in and use it to control the LEDs OR even simpler use a comparator that can connect directly to the battery.

This is a simple application, the thread length is getting out of proportion  

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Rob

There's no need to switch "between" solar and light.

Assuming you have a proper regulator all the battery charging stuff is handled which just leaves the lights, so my earlier comments hold.

As Altairlabs said the reverse polarity diode should be in the panel and/or the regulator but it's probably worth checking it is.

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Rob

If that's all you are doing an Arduino is way overkill.

I would think there are a 100 ways to do this, I'd use a comparator with feedback to give some hysterisis, followed by a transistor if it's a large relay.

With correct resistor choice maybe even just a transistor.

Having said that the Arduino (or any processor) can be programmed to stop the relay oscillating when the light level is on the threshhold, I'd put a stand alone ATtiny85 in there, it's only 8 pins and cheap as chips.

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Rob

ardA dig pin 10 ----(wire)---(1k resistor)---(wire)---ardB dig pin 10

That's fine, no need for GND.

between 13 and ground...got like 13 ohms

But was one of the pins set as an output? You can't really measure that properly and anyway with the above circuit you don't need to.

It doesn't sound like a hardware problem, I think you need to post some code.

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Rob

I gather this is the "three pins" you mentioned in the other thread.

It will work but needs five pins to transfer only 3 bits of data, not very efficient but should be pretty fast.

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Rob

Is there any way you can test the DTR/RST signal to verify that it's working? Do you have a logic probe? that will tell you in a second.

Another way may be to set the LED on pin 13 ON (using a program uploaded normally), then try to program. If the uC gets reset the LED will go off.

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Rob

To get all these devices working together you must already have a protocol in place that addresses them, handles master/slave polling etc.

If so then it's a small step to add a "program" command that downloads the data to your boot loader. I would think the way to do it would be for the master to accept a HEX file from the PC and ship it (either directly or converted back to binary format) to the slave being programmed.

OK, cross posted there, I see you don't want master/slave.

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Rob

7805 based 5V PS circuits, but they aren't they going to limited to around 18V input and about 1A?

Yes, and even then they will get VERY hot without heatsinking. A switching reg is much better here.

Is an LED necessary to drain the caps when off, or will the devices do that?

Not necessary but often good as a convenient "power working" indicator.

The drawing looks OK I think, I doubt all the caps are needed but they never do any harm either.

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Rob