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I'm building a simple RS232 data logger with the Sparkfun OpenLog and a SEEED RS232-TTL adaptor. I'm powering it with a 9 volt battery and a 7805 voltage regulator.

It's dead simple. I built it on a breadboard first and determined that TX-TX and RX-RX connections are called for. I logged several files on the breadboard then soldered it all up. Now it's not working, sigh.

When I power it up both lights will flash rapidly for about a second and then it settles down to a steady on-off with both lights.

If I delete the config file a new one is created, which shows that it recognizes the card at least.

I've triple checked my wiring and confirmed I have no shorts, and that the voltage is good.

I'm attaching a photo as built. Hopefully it's obvious what's what. The purple trace is ground.

enter image description here

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  • It can be so many things. Be careful when one wire is on the top of another wire, when you solder them the plastic could melt and they could connect. A 7805 without capacitors is an oscillator. You need 100nF at the input and output at least. The Sparkfun OpenLog is a ATmega328P running at 3.3V at 16MHz. That is not okay. It will work in most cases, but it is not okay according to the datasheet. And last but not least: something could be broken.
    – Jot
    Commented Mar 27, 2017 at 4:32
  • Sorry Jot, I don't understand, what part is "not ok"? I've added caps to the 7805 and quaduple checked there are no shorts. Still no improvement.
    – marcp
    Commented Mar 27, 2017 at 13:07

2 Answers 2

Reset to default
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The problem with the circuit was a bad rs232-ttl converter. Not sure how that messed up the openlog, but replacing it fixed the problem.

In the photo above, D1 on the converter is an led which should be normally on.

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If the OpenLog's RX pin is held low for too long at startup, it'll reset to 9600 baud to attempt to recover. A bad rs232-ttl converter could cause this, if the RX pin was being held low. If you need the OpenLog to ignore this, see the ignoreRX parameter in config.txt and the hookup guide.

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