First attempt at Eagle...

So is this "correct" so far?

I am eventually going to add a header for the basic NRF24L module things (so they can be simply plugged in once the code has been uploaded to the MCU).

It is my first ever go with Eagle and it is pretty confusing!

I will use a 5.5V input for the board.

Thanks for any input. I want to smooth out anything I am doing obviously stupidly that I can resolve before making an even bigger mess.

Have you tried routing it yet.
First attempt, its not that a complicated circuit but learning a new PCB programme takes time.

Do you have a specific question ?

EDIT
Ah i see you did
Did you autorute or layout manually.

Difficult to see photo, did you check visually that all the tracks correspond with the schematic ?

GND_2 should be grounded...

Do you really need 16MHz? You could ditch the resonator and it's two caps and run at 8MHz internal clock.

Eagle-wise you can use a "VCC" symbol to make the schematic easier to read just like you used the GND symbol.

Thank you for the quick responses!

It seems to look OK in the board file...the connections seem right.
I did use auto-route. I placed the components manually and then used the auto-route feature.

  1. Will the nrf24 be fine with the 8MHz internal clock?

  2. With the VCC symbol, do I also connect a "pad" to the VCC symbol somewhere on my schematic?

  3. I will be using another Arduino as an ISP to connect to the header. Is my ISP header connections correct?

8MHz should be more than fast enough for nrf modules.

Yes, you will still need a pad for your power connections. The VCC symbol does not represent an actual component any more than GND does.

The more you tell us about your project, the better the chance we can help you avoid a mistake. What power source? What application?

I will have a seperate power source. It is a supercap (5.5V) regulated from a solar PV cell.
The leads from the supercap will feed in to the pads on this board.

I will be adding a DHT22 module, possibly a TSL2561 LUX sensor and then a header for NRF24 module.

The unit will sleep (watchdog?) and wake up every hour. Checks the supercap voltage and sleeps if <3V, otherwise takes sensor readings, send them via NRF24 to another “base arduino” and then goes back to sleep.

I will need to add a form of 3.3V regulator for the NRF board. I am finding it hard to select one!

Updated board and schematic:

Link to bigger pic

Link to Bigger Pic

With internal 8MHz clock, will the arduino need a different bootloader? I've never used 8MHz internal clock. How fast can you bootload with it, 57600?

Use thicker traces for Vcc. Add 2nd 0.1uF cap for Vcc. Do not short Aref to Vcc, that is done internally. Add 10K pullup on Reset.
Draw polygon on top & bottom layers, use NAME command and name them GND.
Add an FTDI header for downloading or serial port debugging. 0.1uF cap between DTR pin and Reset.

Johnny010:
I will have a seperate power source. It is a supercap (5.5V) regulated from a solar PV cell.
The leads from the supercap will feed in to the pads on this board.

I will be adding a DHT22 module, possibly a TSL2561 LUX sensor and then a header for NRF24 module.

The unit will sleep (watchdog?) and wake up every hour. Checks the supercap voltage and sleeps if <3V, otherwise takes sensor readings, send them via NRF24 to another “base arduino” and then goes back to sleep.

I will need to add a form of 3.3V regulator for the NRF board. I am finding it hard to select one!

Updated board and schematic:

Link to bigger pic

Link to Bigger Pic

Remove the wire between AVcc and AREF.
Remove the VCC connection to AREF.
connect VCC to AVCC.
Add a 10k resistor between Vcc and Reset, I also place a diode from Reset to Vcc with a cap 0.01uf from GND to reset. These additional parts (diode,Cap) hold the processor in reset until VCC stabilizes. The diode (anode connected to Reset, cathode(banded) connected to Vcc), discharges the capacitor when power fails.

I would second @CrossRoads recommendations, Use the widest trace width you can. CrossRoads’s recommendation to create ground planes should be followed.

I would also add a 4 pin header for the I2C buss (VCC,SCL,SDA,GND). And I would add an additional couple of pins to the ISP connector, If you change the connector to a 4x2 and add pin 10(SS) and maybe one of the Analog inputs your board becomes more general purpose. This give you a fast and easy way to connect SPI devices.

Chuck.

If you are planning to program it over serial (viat tx and rx pins), or otherwise plan to use Serial (ie, UART - I2C/SPI are fine) you need a crystal for reliable operation - the internal resonator's speed isn't calibrated accurately enough for UART.

Use ground plane and thick traces as noted numerous places above.

The 0.1uf decoupling capacitors (the ones between Vcc and Gnd, and AVcc and Gnd) need to be as close to the pins as possible. Add another 0.1uf cap between Vcc and ground on the other side of the chip for good measure, imo.

What's the plan for what it will do? It doesn't look like it does much now.

Hi,
Are you planning to use a DIP IC socket for the chip?
If so, you will need a different 20pin object, because you will have clearance problems around the IC.

As this is your first PCB, not production, I would recommend an IC socket.

Tom.... :slight_smile:

If you are making the PCB yourself, I would suggest increasing the trace width to 16-20mil for all traces.