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This is my first post here, I hope I'm in the correct area.

This is my problem, I bought this circuit to receive caller ID over protocol DTMF.

I have a few 5V power supplies here, (0.45A ,1A and 4.6A), both (0.45 and 1A) works with my circuit, but the 4.6A doesn't.

Also I tried to use my USB port. It works until I connect my USB printer to the computer, then it stops working. (With "works" I mean, the circuit is able to detect the caller ID, because all of them, turn the circuit on.)

And if I use the power supply of 0.45 or 1A, and connect the ground together with the one with 4.6A or the ground with USB port when the printer is connected, it stops decoding the caller id.

With an USB power bank, the circuit works too, does anyone know what is going on with my power supply?

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  • \$\begingroup\$ A USB port can only deliver a certain amount of current (Max 500mA) so that can be the reason why the printer stop the DTMF decoder to work. \$\endgroup\$ – MatsK Jun 22 at 19:45
  • \$\begingroup\$ but it's on another usb port, and if i use one amperimeter on that device, it doesn't even consume 0.1A, when it is working \$\endgroup\$ – Caio_93 Jun 22 at 19:47
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    \$\begingroup\$ your amperemeter might simply be too slow to see the changing current draw, and just display an average. \$\endgroup\$ – Marcus Müller Jun 22 at 19:54
  • \$\begingroup\$ I rather suspect issues with ground loops or EMI from either the 5 V & 4.6 A power supply and/or the USB printer. It think it is not drawn current related since "And if I use the power supply of 0.45 or 1A, and connect the ground together with the one with 4.6A or the ground with USB port when the printer is connected, it stops decoding the caller id." \$\endgroup\$ – Huisman Jun 22 at 19:56
  • \$\begingroup\$ ok, but why it doesn't work with my 4.6A power supply? \$\endgroup\$ – Caio_93 Jun 22 at 19:57
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The problem is probably interference between the power supply and the telephone line.

Telephone lines and power lines should be isolated from one another, but cheap devices (the DTMF decoder, or the power supply, or both) may skimp on isolation - if it were a circuit with a speaker, you would hear a loud humming noise.

This goes along with the USB connection on your computer. It works until you plug in the printer. The printer can also cause interference.

It might be as simple as a"noisy" power supply (the 5V is more like "5V with garbage on it") or it might be that the isolation is poor and you get what are called "ground loops."

In any case, use which ever power supply works best.


That module is (according to the seller's website and the datasheet of the IC on the module) not a caller-ID module. It is a DTMF decoder with a 4 bit binary output.

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This answer does not attempt to address your real question but is only to clarify your understanding.


This is my problem, I bought this circuit to receive caller ID over protocol DTMF.

As JRE has pointed out, you are confusing DTMF (dual-tone, multi-frequency) with Caller ID.

enter image description here

Figure 1. DTMF frequency matrix. Pressing any button transmits the row and column tones for that button. Image source: SigIDWiki.

DTMF is used to send dialling information and superceded the old pulse-dialling used on rotary dial phones.

Caller ID (caller identification, CID), also called calling line identification (CLID), Calling Line Identification (CLI), calling number delivery (CND), calling number identification (CNID), calling line identification presentation (CLIP), or call display, is a telephone service, available in analog and digital telephone systems, including VoIP, that transmits a caller's telephone number to the called party's telephone equipment when the call is being set up. Source: Caller ID.

This is completely separate from DTMF and does not use DTMF for transmission. As far as I can remember, on analogue lines it is usually transmitted as high frequency (inaudible) data between the first and second ring.

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