Video demonstration of modified MT500: http://www.youtube.com/watch?v=i_FZpVC3boo
Materials needed to build Bluetooth-enabled MT500:
1 – Motorola MT500 Radio, non-working preferred (between $15 and $40 on eBay)
1 – Motorola T215 Handsfree Bluetooth Speakerphone ($40 @ Wal-mart)
1 – Scrap piece of soft 3/16” – ¼ thick foam
1 – Fine gauge wire wrap wire
1 – Cherry microswitch (Radio Shack or DigiKey)
1 – Cell phone which is capable of binding to your Motorola T215 (almost all are, these days)
*Recommended – Ringtone which will add to the effect, such as a sample from the movie where a Ghostbuster is trying to raise a teammate using the radio
Tools needed to build Bluetooth-enabled MT500:
- Phillips Screwdrivers (medium and small)
- Dremel tool
- Metal grinder bit
- Plastic grinder bit
- Cutoff wheel
- Angle grinder with metal cutter wheel (optional, bur recommended)
- Needle nose pliers
- X-acto blade or razor blade
- Soldering Iron (low temp for surface-mounted components and fine wire)
- Low temp solder
- Multimeter (for verifying circuits)
- Goop adhesive or Hot glue
Before you start, it is a good idea to bind and test the T215 with your phone to ensure proper operation.
Steps and photos may vary between MT500 radios due to feature variances, but I had nothing significant to note between my MT500s with varying features.
Step 1: 1) Disassembly of MT500 Radio and Removal of Internal Electronics
Step 2: Remove the back of the radio using a medium Phillips screwdriver.
Step 3: Remove any electronics boards you can get to using a Phillips screwdriver. (remember to keep all external switches and knobs installed, as you don’t need to remove them for this project)
Step 4: Remove the metallic “middle” part of the housing by unscrewing the posts holding it to the face part of the housing using a Phillips screwdriver.
Step 5: Remove any electronics boards you can get to using a Phillips screwdriver. Also, remove the built-in speaker AND microphone assemblies as well as all felt between them and the MT500 housing, as they will not be needed. Be sure to keep the bracket and screw that hold the microphone in place, as you will use this later.
You should now have a 3 piece housing plus battery cover all separated. All switches and knobs should still be in place.
Step 2: 2) Initial Modification of MT500 Housing
Step 3: 3) Disassembly of T215 Device
Step 8: Remove the red microphone in the T215 from its place by wiggling and prying gently. Take care not to wreck the wiring between the microphone and board.
Step 9: Using the fine Phillips screwdriver, remove the screws holding the long circuit board (button/controls) half of the board in place inside the T215. You will notice that the board for controls and the main board are connected with a fine ribbon cable. Take care not to kink or rip this cable.
Step 10: Mark the surface buttons with their function using the outside of the case buttons for reference, as you will be cutting this part of the housing off later.
Step 4: 4) Modification of T215 Housing in Preparation of Fitting It Inside the MT500, and Installation in the MT500 Housing
Step 12: Now, take the control board and flip it over to mount it on the back of the speaker on the main portion of the T215. You will effectively be folding it over to “stack” it taller inside the radio, so it will fit. Using hot glue, glue the control board in place on the back of the T215’s speaker for a secure fit.
Step 13: Now that the T215 body is narrow enough to fit into the housing of the MT500 with the T215 speaker oriented where the original speaker was mounted, use the Dremel grinding wheel to grind any plastic ridges that keep the T215 from mounting flush against the inner face of the MT500 as far away as possible from the MT500’s “key” switch. Also, use needle nose pliers and/or the Dremel to remove the metallic strips mounted in the face portion of the MT500 case and all associated plastic posts or remnants.
Step 14: Cut a piece of your ¼” foam in a circle using the discarded MT500 speaker as a guide. Within the circle you cut for the speaker, cut a hole for the T215’s speaker. This piece of foam will serve to funnel audio from the T215 directly out of the grille for the MT500’s original speaker.
Step 15: Using hot glue, mount the foam in place inside the MT500. Then, glue the T215 in place as far as you can away from the MT500’s “key” switch to leave room for a replacement switch to be added later. Your T215 should be mounted so that you will have access to the battery socket, on/off switch, and charging plug through the MT500’s battery cover once the unit is reassembled.
Step 5: 5) Installing the T215 Microphone and Call Answer Button Inside the MT500
Step 17: Using fine gauge wire wrap wire, lengthen the microphone leads so that the red microphone will reach up and around the T215 to the original MT500 microphone position. A little extra length is okay, just keep it reasonable. Use heat shrink tube or liquid electrical tape to insulate solder joints.
Step 18: Using an X-acto or razor blade, cut the face of the red microphone on the T215 to make it flat. Basically, cut the little “tube” off the end and trim it down in preparation for mounting it in place inside the MT500’s socket using the original microphone bracket.
Step 19: Mount the T215’s microphone in place using the existing MT500 housing socket and bracket with single screw. Make sure the hole for the microphone faces forward so that sound can get directed into it properly.
Step 20: Using fine gauge wire, solder one lead each to the pads of the “call answer” button on the T215 (this should be the button closest to the bottom of the MT500 now). Make these leads about 5-6” just to be safe. This step will allow you to relocate the “call answer” button on the T215.
Step 21: Solder the leads for the “call answer” switch on the T215 to your cherry microswitch or equivalent.
Step 22: Using hot glue or other means, position your cherry microswitch in place so that the post on the MT500’s “key” switch actuates the button on the cherry microswitch. This is the button that will be used to answer and disconnect calls. You may have to use a Dremel to shape the microswitch’s button. You may also have to shim up the switch in place to make it fit properly. You will have to install the switch with care to get it to key properly. Take your time positioning the switch, and test it before gluing it in place.
Step 6: 6) Removing the Battery From the T215 and Mounting It in the MT500 (along With Final Modifications for Proper Battery Fit)
Step 24: You can reconnect the li-po battery and test its function at this point, before closing everything up. I found that reconnecting the battery did not reactivate the T215, I had to plug the T215 into a charger after reconnecting the battery to reactivate it. I don’t know why this is, but don’t fret if your T215 looks dead after reconnecting the battery… this simple step should turn it right back on.
Step 25: Reassemble your MT500 using reverse steps 1-4. Make sure no wires get pinched or broken free. Also, make sure you have room to reconnect your li-po battery once assembled (alternatively, you can reconnect the battery, then reassemble the MT500 around it). This is the time when you can most easily adjust the volume to suit your needs. Adjusting it later simply requires removing the back of the MT500 housing using a Phillips screwdriver. (note: volume settings do remain in memory even when the unit is switched off, so you can set it once and forget it)
Step 26: Using the Dremel grinding wheel, remove one of the rails from the inside of the battery cover to make room for your battery to be installed vertically as shown in the illustration. I found this is the best orientation to keep the on/off switch and charging plug accessible.
Step 27: You can now mount the battery using hot glue, Goop, or double-sided foam tape. Just remember, you may want to remove it later.
Step 28: Replace the battery cover.
Step 7: Operation
• Charge the unit by opening the battery door and connecting to an appropriate charger.
• Amaze your friends by using an appropriately themed ringtone with your phone and answering calls while staying in character at a party or other function. You can even place calls using voice dialing through the modified MT500, if your phone supports this feature.
I built this project, because I volunteer with the Arizona Ghostbusters.
We participate in countless charity events every year, and I figure a build like this one will get a lot of use in a club like ours.