After having installed a Cyberdata SIP intercom system posted here, I recently had a need to replace my own door Intercom system, and began to look for alternatives. I did not want to use the Cyberdata because of its prohibitive price, around $400 USD, which is far too much to spend on a single intercom station, or even SIP for that matter.  This idea struck me because I had recently installed some Grandstream phones in a clients office as temporary replacements while we awaited the rest of their Polycom order. Before the Polycom’s arrived client complained that on more than one of these Grandstream units, the handset failed. What to do with Grandstream phones with non working handsets?

Below are the details of how I hacked a Grandstream  BT102 into a fully functional SIP door Intercom.

First I want to clarify that this is a hack. I accept no responsibility of you fry something. Use this information at your own risk!  This hack does not compare to the Cyberdata unit as it has no remote contact closures nor alarms. For basic SIP communication from your door to wherever, you can see the value it offers. This should work for any BT 101/102. The Grandstream BT 101/102 phone are identical except for the number of LAN ports. I imagine this same hack will apply to all versions of both models but I have not confirmed this. Please note that Ethernet requires only four wires (two pairs) theoretically one could use an additional pair for power, and the remaining pair to trigger a relay as a remote door opener.

Before continuing, consider how you will deliver power to the device located at the door. Something like “The Poor Man’s POE” should work fine if cable lengths are not too long. I personally would skip the adapters and wire the Ethernet cable directly to the power to save space.

In my case, I reused the old intercom housing, as I did not want to deal with the complexities of changing the box. If you are doing a new installation , you will need to spend some money on a custom housing, otherwise you may be able to work from an old intercom housing as I did. The nice thing about a hack is that you may even extend it on to something like a full speakerphone with numeric keypad. The ribbon cable seems well marked on the keypad board, thereby facilitating even more hacks to make something like the one pictured below.

I never liked the Grandstream Budgetone series of phones much. They always seemed to reek of cheap Chinese Plastic. There was never anything special about the voice quality and the speaker phone is quite basic. This basic spekerphone functionality however  is quite useful in our hack.

Grandstream BT101 or BT102 that has working speakerphone functionality. Handset case or other buttons may be broken, as long as the Speakerphone function works and you have access for programming the phone.

What you will need:

Weatherproof box- either new or from Intercom to be replaced as in my case.

Soldering Iron

Grandstream Budgetone BT-101 or BT-102, even if some number buttons do not work or the handset is broke. If the speakerphone can answer a call, it will probably work.

Electrical tape

Tools

Miscellaneous low voltage wire

Single Pole Single Throw, Normally Open momentary contact switch (Call button)

Stand-offs, or mounting hardware

A toothpick

If locating the unit outside- Weatherproof 8 ohm speaker, such as polypropylene rated to 1/2 watt, appropriately sizes to fit the box you will use.

Before continuing

You need to program and test the Budgetone for your particular use. I did this with the unit fully assembled, and established IP Address auto dial calling from the Budgetone to a Zulty’s ZIP (to be used as the Indoor station) . I then established the same from the Zulty’s to the Door phone. Because this hack involves using  only the speakerphone button from the Grandstream, you will have no opportunity later to adjust ring volume etc, so do it before the unit is dismantled. I set the Budgetone to be modded to “auto answer” as well.Also in my test with the Zulty’s in my initial test set up, the Zulty’s would not stop ringing. Because this firmware looks much like Leadtek and 8×8 firmware that I had seen this issue with before, I switched the indoor station test unit to a Grandstream Budgetone BT202, which proved to stop ringing after about a minute. ( this is also an option in these Grandstream phones that you may have to enable) . Also worth noting is that Grandstream’s docuementation here , seems to be inaccurate when configuring IP dialing. and when considering autodialing an IP address. I found that I had to put the other phone’s (destination phone)  IP address in the SIP server field of both phones, then I entered  “1″ in the auto dial field. Of course if you use Asterisk/Trixbox/Elastix/FreePBX this does not apply. With Asterisk you have the added benefit of sending to multiple destinations such as your cell phone which means you could answer the door when travelling and the person at the door has no clue you are not there, unless of course you tell them.

Now to the hardware

First we open the Budgetone by removing the four screws. Once opened we can see that there are three boards on the inside. One for Display, one for buttons and another for the core system. This core system board is the one that interests us, as well as microphone, ribbon cable and the speaker (if our intercom will be located indoors).

If you have tested and are ready to get into it, remove the main board and cut the ribbon cable at roughly the half way point, or more towards the keypad board. We will separate out only four conductors, one pair to activate the speakerphone and another pair to connect the speaker.

The toothpick is used to keep the hookswitch in the on-hook state.

You now need to prepare your board mounting hardware to your box, and test for fit.

Next we need only four wires separated from the ribbon cable. (See Images), to connect speaker and momentary contact switch.

Once the board is mounted and your Call Button and speaker are connected you can test the unit before putting it into actual service.

It is a good idea to test the unit at various stages in the hack. That way if something goes wrong you could hopefully undo you last move.

I am interested in hearing comments about this hack particularly if someone uses it with a numeric keypad.

This entry was posted on Saturday, May 14th, 2011 at 4:41 pm and is filed under Uncategorized. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.