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mk484

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8Instructables113,226Views56CommentsBrisbane Australia
Started as a hobbyist at 9 - built my first crystal radio on one of mum's prized cutting boards (eeek) - Worked in 2 electrical/electronics stores as a teenager - Became a College kid in 1980 studied electronics. Went on to work for the phone company for 5 years. Began a career in Business Equipment sales, service and programming in 1987. Had 2 small businesses in that industry. Taught hobby classes in the mid 1990's Have several telephone and crystal radio projects online. Am a regular...

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  • Homemade Intercom (PBX) With GPIO

    Hi there! Well done to work this out with a PIC controller chip and source code. It becomes complicated when you want to read dial pulses going into a microprocessor, that's why I avoided that approach. DTMF tone dialling may be an upgrade you might want to consider for the future, seeing you've nutted out the coding for all the basic features.My approach to telephone intercoms was much simpler. My first attempt was an A to B link circuit using two relays and a 555 timer chip. I also used 9 volt DC buzzers for each handset to avoid the use of high/dangerous ring voltages. This unit ran quite happily on 12 to 15 volts DC and you could combine old rotary phones with more modern push button models by using a 220 ohm resistor in one leg of the rotary phone line, to provide for 'current shar...

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    Hi there! Well done to work this out with a PIC controller chip and source code. It becomes complicated when you want to read dial pulses going into a microprocessor, that's why I avoided that approach. DTMF tone dialling may be an upgrade you might want to consider for the future, seeing you've nutted out the coding for all the basic features.My approach to telephone intercoms was much simpler. My first attempt was an A to B link circuit using two relays and a 555 timer chip. I also used 9 volt DC buzzers for each handset to avoid the use of high/dangerous ring voltages. This unit ran quite happily on 12 to 15 volts DC and you could combine old rotary phones with more modern push button models by using a 220 ohm resistor in one leg of the rotary phone line, to provide for 'current sharing' between the two phones. A version of this intercom is here on Instructables if you want to check it out.There's also a solid state version elsewhere online, that replaces the relays with optocouplers. Just Google "Link Intercom A to B" and it should pop up.My second attempt used a CD4017B decade counter IC to count dial pulses using optocouplers to square up the dial pulses and interface each phone handset, and a NE 556 dual timer chip to generate dial tone and ring tone for each handset. The phones were wired in parallel (party line) and you could only have one call at a time, but it was great for around the house or small workshop, warehouse, scout den etc. It was called "The Link Telephone Intercom" and can still be found on websites that stole the design and denied me any credit... This unit also used DC buzzers instead of bell current.My third attempt used tone dialling, a simple relay matrix for switching calls, the familiar NE556 dual timer IC for service tones and a true 'ring trip' circuit that detected when a phone was picked up 'off hook' to answer a call. Ring voltage was around 30 volts AC and the handsets used were much more modern TF 200 phones by Telstra. This design was called "The Link P - Privacy Link' and although you could still have only one call at a time, that call was private. The other two phones excluded from the call received a busy tone signal. Last party release reset the Link circuit ready for the next call. This design still used hard wired logic with no processing chip involved.I think you've done really well, but with all such projects, while they have their attributes, they also have their limitations. Try adding service tones and DTMF tone dialling as a possible upgrade in the future - you'll probably enjoy the challenge and the achievement will please your readers. Has anyone indicated that they've built a copy of your design yet? That's always a good encouraging sing.Well done dr research... :)

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  • Cordless Phones Used As Home Intercom

    Hi there,I thought myself that it might be possible to program one of the handsets as a 'master' set only? If Oricom doesn't do that, then you'll have to try something else. Perhaps you could just get a cheap but reliable landline phone and use that for all incoming/outgoing calls, and then keep the cordless phone network separate for internal use only? The good thing about this is that you can add extra handsets if you need them and there's no extra cabling needed beyond the first landline phone socket.I know it seems to be a bit cumbersome, but without paying a lot more money and buying a basic key phone system, which is usually programmable with around a dozen or more options, I don't see any other choice.

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  • Simple Intercom From a Pair of Old Corded Phones

    Thanks. I checked it out and they've completely redone that website and have deleted all of the old projects from years ago. I've got another project for a wired phone intercom so go to my home page here MK484 and have a look at that one...

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  • 2 Phone Intercom With Buzzers...

    Hi! Well yes and no - but there is an earth/ground line wired in. Positive 12 volts is at the bottom of the circuit, where one side of each relay coil join together. Earth/ground return occurs via each individual phone (speech and dialing) circuit, but each phone handset does in fact complete an individual return circuit, as it must, to allow for independent signalling, as well as when both handsets are in the "off hook" condition while both parties are talking. Hope this helps...mk484

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  • Nic Nac Tic Tac Crystal Radio Set - An Ideal Primary School Project...

    Hi Colaris - what I meant to say was that "Trying to drive a low impedance 'load' such as a pair of earbuds, is like trying to drive a mains powered (toaster) with a 9 volt battery - it's not going to happen..."

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