ERSKYTx (was ersky9x) Questions

[Rafit]

Yes,
There are still a couple of boards unspoken for.

-Brent

So I definitely want one There is no private messages on this forum? Please send me any needed info to my email rafit (at) m2p (dot) pl


To post not only spam, i have one proposal for this new board.

It is possible to add connection to additional PPM module? Simple 3 pin connector (ground, Vcc, PPM Out 2) should be enough (if Vcc could be switched off by software it would be perfect). This mod should allow adding extra DIY radio module (FrSky for example). Having two connections to model in that same time give cheap additional channels or more stable connection (redundancy).

[MikeB]

Currently we have the PPM output (that could also be PCM or DSM) that goes to the tx module. The PPM output to the trainer port is a COMPLETELY separate signal, with its own signal generator PWM1(H). This could be used as a second PPM output, just prevents using the trainer input at the same time.
To get another PPM output signal I think it would need to be on PC15, currently used for LCD_A0. This would be on PWM1(L), allowing the trainer input to function at the same time.
PWM0 is used for LED backlight brightness.
PWM2 could drive the haptic signal.
PWM3 is the main PPM output.
If PWM2 is not needed for the haptic, then PA2, PB4 or PC20 may be configured to use the PWM2 output.

I would be quite happy to say if you want two PPM output drives then you cannot have the trainer input as well, or is this too much of a restriction.

Mike.

[SkyNorth]

So you want a spot for a connector to access the PPM output?
There is a second PPM output on the trainer port.

-Brent

[MikeB]

Is it worth/possible to put a 3-pin header with +v, signal and ground on this PPM to the trainer socket then?

Mike.

[Rafit]

I would be quite happy to say if you want two PPM output drives then you cannot have the trainer input as well, or is this too much of a restriction.

If you want many outputs channels, then probably you are using something extra (like tilt/pan sensor connected to your video glasses).
I would rather trade it for LED backlight brightness control or haptic, than lose input via trainer port.

[MikeB]

This would be a configurable option. You don't lose the trainer input, only cannot use it if you are using the second PPM output.
I've lost track of whether we have any spare pins now, I thought we had pretty well used them all up. If there is a spare that could be used instead of LCD_A0 on PC15, then PC15 could be made available, if it will track on the board, as an extra PWM controlled output for another PPM signal. Then space need to be found for another 3-pin header.

@rafit, if you want to get into the ARM code, http://code.google.com/p/ersky9x/ is where the software for this board is stored.

Mike.

[SkyNorth]

Well it possible to free up LCD-A0 line for the 2nd ppm output...

BUT

The only free pin is PA25 , it is the extra lcd/bus chip select line.

I can move it to LCD-A0 , but it is not on Port C , but Port A ...will this be a problem?

The RTC crystal used up the only other two pins on that side of the chip.

-Brent

[SkyNorth]

I have been playing with the Idea of adding a i2C port expander.

I wanted to have more inputs available for switches and pots...but with all the built-in features we have added , there are very
few port pins left for general I/O use. The port expander chips are expensive for what they are ...so I'm looking at a ATTiny20 AVR
microprocessor.

It comes in a small 14 pin SMT package , and has a I2C slave interface.

I can bring 7 port A pins and 1 portB pin to a 10 pin header.

This would allow for 8 switch inputs , or up to 7 more A/D inputs , or some more PWM outputs.

The chip is under $1 , I think this would fill the spot on the pcb better than a RTC clock chip + crystal .

And it could be programmed by the end user for thier own special functions.

-Brent

[MikeB]

The only free pin is PA25 , it is the extra lcd/bus chip select line.
I can move it to LCD-A0 , but it is not on Port C , but Port A ...will this be a problem?
-Brent

Being on port A is no problem. Losing the second chip is a shame, it might have been useful for larger displays in the future, but there are probably enough 128x64s that will fit one or other connectors.

Mike.

[MikeB]

I wanted to have more inputs available for switches and pots...but with all the built-in features we have added , there are very
few port pins left for general I/O use. The port expander chips are expensive for what they are ...so I'm looking at a ATTiny20 AVR
microprocessor.

I can bring 7 port A pins and 1 portB pin to a 10 pin header.

This would allow for 8 switch inputs , or up to 7 more A/D inputs , or some more PWM outputs.
And it could be programmed by the end user for thier own special functions.

-Brent

Sounds good, I assume the required programming pins will be on the header (or somewhere), including reset and power, to allow it to be programmed.
I thought we were running low on i/o pins, you would think with 100 pins there would be enough!
And the I2C port is on a header so more I2C devices could be added externally.
Provided it is guraanteed low at start up, the ERASE input can be used as another I/O. It powers up as ERASE, but can be changed under program control for another function, so as long as we can hold it a 3.3V at power on, we can still erase the chip.

Mike.

[SkyNorth]

I could use the ERASE pin on the EXIT key ... It could not be high (unless pulled high)
and if pressed it goes to ground...

-Brent

[MikeB]

I'll give it a test to make sure it works.

Mike.

[SkyNorth]

I will swap the LCD-A0 , and PA25 lines. I will leave the connection to the expansion header , as well
as a new connection as a PPM-out. This way we can choose between a second chip select , or a second ppm output.

The ATtiny20 , needs to be at 5V to program ..so I need a way to isolate it while programming.
The part comes in a 14pin dip , 14 pin SO package and 14 pin TSSOP package.

The dip package is a little big , but might be nice since it could be socketed.

-Brent

[SkyNorth]

I was just checking for different AVRs...

I found a ATTiny24 ... same package as the attiny20 , but this built-in self programming.

It costs a little more ,but that it has self - programming . is worth it.

-Brent

[MikeB]

I was just going to recommend that, It programs on 1.8V as well from external serial. Over here, the ATTINY84A comes up as cheaper, same chip just more memory!

Mike.

P.S., It occured to me this chip (whichever version) could handle the quadrature encoder, just supplying the ARM with position data.

[SkyNorth]

Yes,
Also in theory , I could Isolate it from the supply , and provide a connector for a backup battery.
and provide a spot for a 32khz crystal ..
just thinkin'
-Brent

[MikeB]

I've often found that thinking is dangerous
If you do add the 32kHz xtal, I don't think we would need the one on the ARM as well. THe on-chip RTC may be clocked from the RC SCLK clock, and kept in time with the time from the tiny24 for accuracy, unless you want to have 2 32kHx xtals.

It would provide a replacement for the RTC.

Mike.

[MikeB]

I've been researching the Tiny24. If you fit a 32kHz xtal, then that will be the clock speed it will run at, it only has the one xtal oscillator. This will not be fast enough to handle the I2C really. I'm looking, but I think you would have to go to the Mega48/88/168 to get a device with a separate 32kHz oscillator. Just looking at the Tiny87, 20 pins, includes a 32kHz oscillator for timer 0, the only Tiny device with it. A bit more pricy possibly, but with a battery backup could provide RTC, expanded I/O and the RAM could store power on time accurately without worrying about wearing out the EEPROM.

Mike.

[SkyNorth]

That was my thinking ... We get a RTC , memory , Extra A/Ds , pwm , timers.

And we gain back two ports from the crystal.

I'll take a look at the other chip ...I think this is the way to go...to get the most bang for the buck..

-Brent

[SkyNorth]

Here is what I have ,

Will this work for the supercap ?

How do we know when the power is out?

-Brent

[MikeB]

Looks OK, that Supercap is 0.06F isn't it? I'm looking at how much current the tiny87 will take when asleep, but the 32kHz oscillator is running. I have a suspicion the cap won't be large enough to run the chip for very long, but I need to check.

Mike.

[SkyNorth]

I was wondering that , maybe just a 2pin plug , then a external AAA cell could be used.

What about the leakage through the I2C pins?

-Brent

[MikeB]

I can't find a definitive definition of the current consumption in 'power save' mode, the mode we need to use. It could be several uA. At 1uA, I reckon a 0.06F cap will last about 17 hours, discharging from 3 to 2 volts. A 50mAh battery will last, in theory, 5 years!

Mike.

[SkyNorth]

The best I can do is put in a 2 pin socket. and leave the battery to the end user.
It will also help with the rising cost.

Do I need top use a port pin to sense for main 3.3V power?

If the main power gets shut off , how do you know to go into power down.?

-Brent

[Reacher10]

I'm just following along with you guys. I was thinking from the beginning to just let the user put in their own battery
for the real time clock.

Could the on-board battery used as well but have a cut off if the voltage drops to what the user sets?

By having both the user could select which battery to use and set a cut off for the on board voltage.

If 50Ma would last 5 years, the on board battery should be fine. Hell I use the trustfire 2500Ma and according
to my calculations based on what you said it should last...well...like a really really long time.

[MikeB]

A pin might be useful, but I think the I2C will do it for us. It's open collector/drain, with a pullup to the main supply. So if SDA and SCL are high, we have main power, but if they are low we don't.

A 2 pin header is probably best, will you leave the diode charge circuit in? Or could you make it a 3 pin header, with the diode charge on one pin, the diode supply to the attiny on another and the third ground. Then we could use an external supercap (1F say), or a battery etc.

Mike.

[SkyNorth]

I was going to use the main battery , but it could kill it over time,also
a lot of people remove the battery for charging......so a connector would be best.

Mike - do we need a interrupt line to the ARM? or will you poll the AVR?

-Brent

[MikeB]

I'll poll it, if necessary we can use 'multi-master' mode on the I2C and the 'tiny can send data to the ARM.

Mike.

[SkyNorth]

Mike , I think we are out of room....well there's always the other side ..

Here is what I have come up with

What does everybody think?

-Brent

[cre8tiveleo]

Looks good .. I think I see a typo though...




Kidding...




I have a question, are the two screen addressable seperately? Can each one display different data if desired? If you had both hooked up? It's just a question...