Pull-up resistors for AXE033 / AXE133Y

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jikmar

New Member
I have put together a project using a hybrid display formed from The display from an AXE133Y (OLED) and the i2c driver board from an AXE033. It seemed like a good idea at the time as I had a previous project which used the AXE033 on i2c and I wanted to duplicate it. I also fancied using the OLED screen for its improved 'magpie' appeal.

It works well until it tries to interrogate the DS1307 clock, when it has a tendency to (sometimes) reset the picaxe.

I notice from page 6 of the AXE033 manual that, " the 4k7 resistors pull up resistors are pre-soldered onto the AXE033 LCD
module. Therefore additional external resistors are not required."

Where are these resistors, and are they on the AXE133Y oled board? If not can I put them on? It would probably be easier to put them onto my AXE022 board - would this be ok?

Thanks.
 
N

nick12ab

Senior Member
jikmar said:
I notice from page 6 of the AXE033 manual that, " the 4k7 resistors pull up resistors are pre-soldered onto the AXE033 LCD
module. Therefore additional external resistors are not required."

Where are these resistors, and are they on the AXE133Y oled board?
Click to expand...
No, they are on the AXE033 PCB.
 
N

nick12ab

Senior Member
jikmar said:
It works well until it tries to interrogate the DS1307 clock, when it has a tendency to (sometimes) reset the picaxe.
Click to expand...
Did you short the PWR jumper on the AXE033 PCB? This bypasses the diode which when not bypassed causes more problems with the AXE033-mounted DS1307 than any other component. This is because the diode can lower the power supply voltage to around that of the shutoff voltage for the DS1307 i2c pins when a fresh cell is fitted in the cell holder.

Also make sure you do have a cell fitted, even if is a flat one.
 
W

westaust55

Moderator
jikmar said:
I have put together a project using a hybrid display formed from The display from an AXE133Y (OLED) and the i2c driver board from an AXE033. It seemed like a good idea at the time as I had a previous project which used the AXE033 on i2c and I wanted to duplicate it. I also fancied using the OLED screen for its improved 'magpie' appeal.

It works well until it tries to interrogate the DS1307 clock, when it has a tendency to (sometimes) reset the picaxe.

I notice from page 6 of the AXE033 manual that, " the 4k7 resistors pull up resistors are pre-soldered onto the AXE033 LCD
module. Therefore additional external resistors are not required."

Where are these resistors, and are they on the AXE133Y oled board? If not can I put them on? It would probably be easier to put them onto my AXE022 board - would this be ok?

Thanks.
Click to expand...
Can you confirm that you are using the i2c comms for both the display and the RTC.

As already mentioned by nick12ab, the pull up resistors are located on the display "back-pack" board that you have taken form the aXE033.

Are you using the I2CSLOW parameter (not I2CFAST) having the DS1307 in the circuit.

Do you have the AXE033 jumper set to i2c mode?

If the i2c bus becomes "locked-up" then the PICAXE will reset after 2.3 seconds due to the internal watchdog timer.

Have a read of this thread as well: http://www.picaxeforum.co.uk/showthread.php?9726-Troubleshooting-unwanted-picaxe-reset
 
N

nick12ab

Senior Member
jikmar said:
No, the instructions suggest this is not necessary for a 5v supply. Do you think it is still worth putting the link in?
Click to expand...
Yes, put the link on. The instructions are a bit misleading and at first made me scared to do it but the DS1307, PIC16F819 and the provided LCD/OLED are all rated to run at 5V so it will not cause any damage.

For the DS1307: The nominal power-fail trip point (VPF) voltage at which access to the RTC and user RAM is denied is set by the internal circuitry as 1.25 x VBAT nominal. If the diode is dropping the supply voltage down to 4.3V and a fresh cell is 3.3V then that gives a VPF of 4.125V. As the 1.25x figure is only nominal and according to the datasheet it can be between 1.216x and 1.284x, VPF could actually be anything up to 4.24V which is only a bit below the power supply voltage so if the voltage sags slightly access to the DS1307 might be denied.
 
J

jikmar

New Member
Thanks to Nick12ab and WestAust55,

I think you were both on the right trail. Removing the DS1307 chip itself stops the resetting, and soldering in the wire link for 'power' seems to fix the problem completely.

Thank you both for a sharp insight into the problem.
 
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