Jump to content

Reading data from 3.5mm audio jack

Recommended Posts

@@roadrunner84 The circuit can be used for on-off. When a signal is not present, the period is greater than a boundary value. When it is present, the period is less than the boundary value.


The advantages to this type of circuit over many alternatives are simplicity and versatility. It can be used for FSK, OOK, and can be used for standard serial, FM and MFM self timed communication, among others. For FSK and OOK, a minimum number of cycles can be used per bit, often only one, if the channel otherwise doesn't affect phase with frequency or have significant filtering.


The drawback is that, in applications where you NEED to use a carrier (such as On-Off or FSK) due to channel properties, the processor has to do timing at higher than bit rate frequency and can't treat the input using standard UART tools.


The historical application that comes to mind (1977) for this is the TRS-80 cassette, where, rather than use the Kansas city standard, FM (and MFM) were used with a standard audio cassette recorder. Quite reliable and tolerant to timing variation at one transition per bit. Similar methods were used into the mid-1980's by several other manufacturers.

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...