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  1. #1
    Member Dave-S's Avatar
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    Default DTMFOUT association with Oscillator frequency

    Have a project which detects power supplies and temperatures of equipment and sends alarms via landline telephone, working ok on a 16F877A. I need to expand this project and require more pins so we have moved it to a 18F87K90 but have a couple of problems.

    1. The DTMF tones do not work, they are not recognised by the telephone line. The 16F877A was running at 20Mhz and the 18F87K90 is running at 64Mhz, should not the DTMF tones be the same? listening to them they are going a lot slower on the 18F87K90, so I altered the ONTIME/OFFTIME but it still does not work, what is the relationship to the Oscillator?

    1. Using NTC thermistors for temperature measurement, the 16F877A was 10 bit ADC (1024 counts) where the 18F87K90 is 12 bit ADC (4096 counts), it gives better resolution. They are connected to panel via plug and socket with + 5 volts to one side of Thermistor and the other side is connected to Port pin ADC/ a resistor connected to Ground. When a socket is not in use it works ok on the 16F877A, readings are zero counts, but on the 18F87K90 it works sometimes but occasionally brings up an alarm with a count of around 6554. Where can it get a count of that value from? The pin with nothing plugged in is connected to Ground via 10k resistor so should be zero. I have got around the problem at the moment by setting alarms between two values avoiding anything over 6000.

    Any Ideas would be helpful thanks,
    David

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    Junior Member pe1pme's Avatar
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    Default Re: DTMFOUT association with Oscillator frequency

    It is next to impossible to use a PIC as a DTMF generator bacause of the very tight specifications of the phone system! I should use a specialized IC for that job, like the CD22859e, the TP5089 or the HT9200A or B. The first two and the 9200B are parallel input (7 or 8 pins!) and the HT9200A has a serial input (two extra pins)
    To be OLD and WISE you must first have to be YOUNG and STUPID!

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    Member Dave-S's Avatar
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    Default Re: DTMFOUT association with Oscillator frequency

    Quote Originally Posted by pe1pme View Post
    It is next to impossible to use a PIC as a DTMF generator bacause of the very tight specifications of the phone system! I should use a specialized IC for that job, like the CD22859e, the TP5089 or the HT9200A or B. The first two and the 9200B are parallel input (7 or 8 pins!) and the HT9200A has a serial input (two extra pins)
    I have the HT9200A which I tried but could not work out how to send 5 bytes, see my previous Post HT9200A http://www.protonbasic.co.uk/showthr...TMF-to-HT9200A. It works fine on the 16F877A, with a filter.

    David

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