I have a small system with a ATtiny84 and an RFM12B module that transmits data.

The thing is it only transmits when i touch both GND and +VCC.. no matter what component it is on.

Do i need mere caps or what is the problem? i checked the voltage levels and everything which is fine! Is it because of capitance or what is the solution?

Here is a wiring diagram of the system. enter image description here And a picture enter image description here

  • \$\begingroup\$ Are you using an antenna? \$\endgroup\$ – Andy aka Nov 16 '15 at 14:37
  • \$\begingroup\$ The circuit diagram does not appear to show the RFM12B. \$\endgroup\$ – Andy aka Nov 16 '15 at 14:52
  • \$\begingroup\$ The trx433s is a type of rfm12b. And no antenna. \$\endgroup\$ – Mads Gadeberg Nov 16 '15 at 14:54
  • \$\begingroup\$ @Andyaka will you make a answer to get the points? \$\endgroup\$ – Mads Gadeberg Nov 16 '15 at 14:57
  • 1
    \$\begingroup\$ I did an answer a minute ago. \$\endgroup\$ – Andy aka Nov 16 '15 at 14:57

Try using an antenna: -

enter image description here

Basically the RF transmitted is probably present as a few millivolts on the power rail and earth. Touching either of these turns your body into an antenna.

And don't forget decouplers as mentioned by JRE


You are missing the bypass capacitors on all of your ICs.

A quick check of the documents for the ATtiny84 didn't show a recommended value, but it does mention that bypass caps are needed.

Start with a 0.01µF cap as close as possible to the VCC and GND pins of the ATtiny. You will probably want to put one on the Op-Amp as well. The RF module probably already has one, but it couldn't hurt to put one on it as well.

The biggest problem, though, is the one for the ATtiny. Fix it first, then you will probably find that you are getting strange values from your straingage - bypassing the op-amp will then fix that.

  • \$\begingroup\$ Nice.. its not really my area this electronics world.. how big would you suggest they have to be? Does the datasheet for the components say how big? \$\endgroup\$ – Mads Gadeberg Nov 16 '15 at 14:17
  • \$\begingroup\$ @MadsGadeberg Read the data sheet to find out. \$\endgroup\$ – Andy aka Nov 16 '15 at 14:36
  • \$\begingroup\$ Does not contain the information.. \$\endgroup\$ – Mads Gadeberg Nov 16 '15 at 14:37
  • \$\begingroup\$ I now mounted a 22nF across the tiny and across the rf module with the same result as before. Any other suggestions? \$\endgroup\$ – Mads Gadeberg Nov 16 '15 at 14:49
  • \$\begingroup\$ As @Andyaka asked above - Do you have an antenna connected to the RF module? \$\endgroup\$ – JRE Nov 16 '15 at 14:54

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