ZX-328 AVcc

[dlh]

I have an application using the ZX-328 where I would like to read 2 ADC values. My PCB must fit in very limited space and I cannot see anyway to add the choke and capacitor recommended on AVcc.

How important are these?

The ADC readings are not critical. One will grab the RSSI output of a RF Receiver (which uses the RX3310A from Princeton technology) and the other will measure the signal strength of another input. Absolute values are not important - in both cases it will be more of a strong/average/weak or maybe just good/poor indicator.

[dkinzer]

How important are these?

They are recommended by Atmel in applications where the analog section (ADC and/or analog comparator) will be used. Atmel also recommends a filter capacitor on the Aref pin. It is interesting to note, however, that the Arduino Duemilanove does not have the L-C filter on AVcc but it does have the filter capacitor on Aref.

[dlh]

I had noticed that on the Arduino. I put them in my Zaduino designs.

Have you had a chance to look at my Zarduino page? Any input?

[dkinzer]

Have you had a chance to look at my Zarduino page?

I did - looks good. I assume that the Zarduino 28 and 40 boards could also be used with any pin-compatible 28-pin and 40-pin AVR chip (including A, P and PA variants). If that is true, it's probably worth mentioning.

[table][row]28-pin[col]mega48, mega88, mega168, mega328[row]40-pin[col]mega164, mega324, mega644, mega1284[/table]

[dkinzer]

Have you had a chance to look at my Zarduino page?

Also, if you have the space, it would be a good idea to add the Atmel 2x3 ISP header (0.100" centers) and, on the Zarduino-40, even a JTAG header. For JTAG, you need a 1x4 header laid out as below plus Vcc and Gnd pins (provide these on a 1x2 header).

[table][row]TCK[col]pin 24
[row]TMS[col]pin 25
[row]TDO[col]pin 26
[row]TDI[col]pin 27[/table]

[dlh]

Thanks for the input. I assume all the pin-compatible megas can use the Arduino bootloader.

I'll look at the ICSP and JTAG headers. I was thinking mostly on ZX lines and, while I did not think it necessary, did include a 1x6 ICSP header. I think there's room to make it 2x3 without dislodging anything. I can probably fit the JTAG header above the DB-9.

Where, in relation to the ICSP header and JTAG header should I put the Vcc & GND header. I've seen 2x4 ICSP with those added.

[dkinzer]

I assume all the pin-compatible megas can use the Arduino bootloader.

Yes but they can also use any other bootloader or no bootloader at all.

For people that want to use the board in a non-Arduino way, the ICSP header is needed to allow them to either program their own bootloader or to program the application itself if no bootloader is used. The Atmel standard 2x3 ICSP header is more convenient than a 1x6 header since the Atmel programmers have a 2x3 female IDC connector. The pinout of a 2x3 header should be as shown below (looking down from the top).
[table]
[row]MISO[col]1[col]2[col]Vcc
[row]SCK[col]3[col]4[col]MOSI
[row]Reset[col]5[col]6[col]Ground[/table]

[dlh]

I have an application using the ZX-328 where I would like to read 2 ADC values. My PCB must fit in very limited space and I cannot see any way to add the choke and capacitor recommended on AVcc.

Well, by nudging components and traces this way and that way, I was able to squeeze the inductor and 0.01 cap onto my PCB. It already had the 0.1 cap. So, alls well that ends well.

[dlh]

[table]
[row]MISO[col]1[col]2[col]Vcc
[row]SCK[col]3[col]4[col]MOSI
[row]Reset[col]5[col]6[col]Ground[/table]

Which side should be towards the board edge - MISO or Vcc?

I'll just provide solder pads. Those who need it can solder in the header.

[dlh]

The Zarduino-28 and -40 now have 2x3 ICSP pads and the -40 has 1x4 pads for JTAG. The web page images reflect the changes. I'm not clear whether the Vcc & GND you suggested should be associated with JTAG or can just go anywhere there's some free real estate.

[dkinzer]

I'm not clear whether the Vcc & GND you suggested should be associated with JTAG or can just go anywhere there's some free real estate.

The Vcc/Gnd pins can be anywhere that is convenient.

[dkinzer]

Which side should be towards the board edge - MISO or Vcc?

It doesn't matter. The programmer connects via a ribbon cable terminated with a female IDC so it is easy to adapt to any orientation.

[dlh]

Which side should be towards the board edge - MISO or Vcc?

It doesn't matter. The programmer connects via a ribbon cable terminated with a female IDC so it is easy to adapt to any orientation.

I looked at the Arduino I still have (I gave the UNO to a grandson who is learning C++) and put pin 1 (MISO) away from the edge, as it has it.

[dlh]

One of my first shields is a Serial I/O board that will have 1 hardware USART (when used with Zarduino-40) and 4 software UARTs with one configurable as RS232/485. Of course, it's exact capabilities will depend on the system board.

I want all to have RS232 voltage levels even with 3V3 system voltage. I've found the Linear LTC1348 which looks promising and handles 3V3 and 5V, but uses terminology that I find alien after years of using ST232A.

They have Drivers and Receivers. Am I correct in assuming drivers are RS232 outputs and Receivers are RS232 inputs?

Any other chips that might be a better fit?

[dkinzer]

Am I correct in assuming drivers are RS232 outputs and Receivers are RS232 inputs?

Yes. A driver is a device that takes a logic level and converts it appropriately for driving an external line of some type (e.g. RS-232, RS-485, etc.). A receiver performs the opposite conversion.

Any other chips that might be a better fit?

I've used the MAX3232. For this device operating on 3.3V to 5.0V the capacitors need to be different than the "normal" 100nF. See the datasheet.

For 3.3V only operation, the ADM3202 can be used.