Troubleshooting Telephone Dialer Misdialed Numbers - Holtech Brand

  • Thread starter Phrak
  • Start date
In summary: That's a pretty long duration tone. So if you're generating a DTMF signal at a lower frequency, you're probably not going to see an error. Maybe try a 10khz or 5khz tone.The datasheet quotes a tone error of 0.74% of the worst case generated... and that was with a toneburst of 16khz. That's a pretty long duration tone. So if you're generating a DTMF signal at a lower frequency, you're probably not going to see an error. Maybe try a 10khz or 5khz tone.
  • #1
Phrak
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I have a friend with a telephone dialer (brand name Holtech) in his design. Some numbers are getting misdialed. We suspect the line interface circuit.

Does anyone have topology and component values for the transformer and other components typically used? It has to meet the interface requirements.
 
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  • #2
I may have that in a book at home. I'll make a note to check when I get home from work.

Are you able to see a pattern in the misdials? Do you have access to analyzers that can help you see what is wrong? Does the autodialer have an option to slow down its dialing (the length of each DTMF tone), and does that help?
 
  • #3
berkeman said:
I may have that in a book at home. I'll make a note to check when I get home from work.

Are you able to see a pattern in the misdials? Do you have access to analyzers that can help you see what is wrong? Does the autodialer have an option to slow down its dialing (the length of each DTMF tone), and does that help?

The dialer is a single chip that takes a oscillator and interface. I'm afraid I don't know a lot of details, but it's an integrated package that looks for dial tone, then dials, then waits for either pick-up or busy. I believe pick-up might be signaled by a ~16 KHz burst, then throughputs a recoded message.

I don't know about a pattern. I'd like to see a scope on it too, but it's 70 miles away. No frequency analyser is available.

I think the interface design involved too much guess-work, and not enough research.
 
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  • #4
Phrak said:
The dialer is a single chip that takes a oscillator and interface. I'm afraid I don't know a lot of details. I'd like to see a scope on it too, but it's 70 miles away. No frequency analyser is available.

I think the interface involved too much guess-work, and not enough research.

Would you be able to post a list of some of the misdial patterns?
 
  • #5
berkeman said:
Would you be able to post a list of some of the misdial patterns?

No, sorry. I'll see If I can get some.

I found the Holtek (corrected spelling) website though. http://www.holtek.com.tw/english/products/default.htm"

I'm going to have to get the part number. Otherwise we're going on too much iffy information.
 
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  • #7
berkeman said:
Brought my old phone electronics book into work:

https://www.amazon.com/dp/B000RRHZCW/?tag=pfamazon01-20

Brings back memories flipping through the pages!

You and my friend might have some things to talk about. I believe a telephone circuit was his first design. It was something on the receive-side involving way too many wire-wrapped PLLs and other stuff sometime in the 1980s. This current design is 7x4" of realestate! Good grief. The reason, from what I gather, is that ICs for these sort of circuits have come and gone as OMC devices, so it's built-up from pieces involving the dialer, 5 PLLs and 3 DPST relays to switch various transmitters and receivers in and out.

I'm afraid I'm only getting really sketchy information on this problem. The troubleshooting data base consists of calling one long distance cell phone and one local land-line. The dialer connects to the local land line OK. Dialing the cell phone returns a busy signal. The busy signal is real.

Stay tuned for more if you can take it. :uhh:
 
  • #8
Interesting. What about cell phones on other carriers? Verizon versus AT&T versus whoever... I once had a problem accessing my work voicemail mailbox using my cell phone -- the password I had on the mailbox included a "1" digit, and for some reason, that was not making it through. Changing the password to avoid the "1" fixed my access problem. (A very experienced IT person at my work told me of the 1-problem and cell phones)

There must be a standard quality measure (frequency tolerances and SNRs) for DTMF signalling. Maybe even some test instrumentation that could be leased or borrowed. Maybe some test labs have the equipment, and could test the device to give your friend a report that could help him debug the problem. Yeah, look for telcom testing labs... I think there are several here in Silicon Valley.
 
  • #9
I'll let he know about the services. That's weird with the '1' access number. I gave him my wife's Verizon number to call. Don't know if he tried it or not. Either that or it didn't work either. I'm going to recommend sending tones over a longer time span to give the receiving circuits at the exchange longer to lock-on. It's worth a try.

He's using the HT9320 IC, btw, http://www.holtek.com.tw/english/docum/comm/9320.htm"

The datasheet quotes a tone error of 0.74% of the worst case generated frequency.
 
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1. What is a telephone dialer and how does it work?

A telephone dialer is a device that is used to enter and transmit telephone numbers to make a call. It typically consists of a keypad and a microcontroller that converts the numbers into electronic signals and sends them to a central office or exchange to establish a connection with the desired telephone number.

2. Why are misdials a common issue with telephone dialers?

Misdials can occur due to a variety of reasons, such as human error in entering the numbers, faulty keypads or microcontrollers, or interference in the transmission of electronic signals. Additionally, some telephone dialers may have a small keypad that can be difficult to use, leading to accidental misdials.

3. How can I troubleshoot and fix a misdial issue on my Holtech brand telephone dialer?

The first step is to check for any visible damage or malfunctions on the keypad or microcontroller. If everything appears to be in working order, try cleaning the keypad to remove any dirt or debris that may be interfering with the buttons. If the issue persists, try resetting the dialer by unplugging it from the power source and then plugging it back in. If the problem continues, it may be necessary to contact the manufacturer for further assistance or consider replacing the device.

4. Are there any preventative measures I can take to avoid misdials on my telephone dialer?

Yes, there are a few things you can do to reduce the chances of misdials. First, make sure to enter the numbers slowly and carefully, double-checking each digit before pressing the call button. You can also try using a telephone dialer with a larger keypad or one that has a feature to confirm the number before dialing. Additionally, keeping the keypad clean and free of debris can help prevent misdials.

5. Can misdials on a telephone dialer be a security concern?

In most cases, misdials on a telephone dialer are not a security concern. However, if the misdial connects you to a different number than the one intended, it is important to hang up immediately and not disclose any personal or sensitive information. It is always a good idea to confirm the number before making a call and to be cautious when entering personal information over the phone.

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