Simulation of Bel/Escort SmartCord function...

[MEM-TEK]

Hi everyone,

I have created a circuit simulation which demonstrates the basic functionality of the Bel/Escort SmartCord. This simulation is easily viewed in the java based circuit simulator created by Paul Falstad. Following is a screen shot of the SmartCord simulation.

The circuitry on the blue background is the actual SmartCord circuitry, but with the addition of a 5K potentiometer (to the left of the green power LED) so that you can see how you can modify a SmartCord in order to dim its two LEDs. You can adjust this added potentiometer by moving the Resistance slider in the circuit simulator and then watch the LEDs dim or brighten.

Everything to the right of the SmartCord circuitry merely is simulated circuitry within a Bel/Escort radar detector. This simulated RD circuitry was created in order to simulate the voltages and current flows which I measured when testing a SmartCord which was plugged into a Bel/Escort RD. I even added a RD power switch which you can click on to turn on and off the simulated RD circuitry.



The whole point of this SmartCord simulation is to make it easy for you to design your own accessories which could be used instead of a SmartCord. Just keep in mind the following:

-- Whatever you hook to the black Alert wire which goes into the RD's power jack, it must have an inline resistor of at least 470 Ohms to limit current flow and must present a positive voltage of no more than 12V.

-- Whatever you attach to the yellow Mute wire which goes into the RD's power jack, it must have an inline resistor of at least 470 Ohms and must draw current towards ground.

With the above info and this circuit simulator, you can then design neat stuff like multiple LED alert bars, stereo mute circuits, Piezoelectric buzzers, or whatever.

There also are two other connections within a Bel/Escort RD's RJ-11 power jack. I suspect that one carries data. I don't know what the other one is used for or if it is used at all.


To view and play with the SmartCord simulator circuit, first you need to click on the following link which loads Paul Falstad's circuit simulator Java applet:

Circuit Simulator Applet

Then in the applet you need to click File --> Import and paste in the following circuit code. Copy and paste in everything between the two lines of asterisks:

**********************

$ 1 5.0E-6 7.943983955226134 51 5.0 50
R 80 128 32 128 0 0 40.0 12.0 0.0 0.0 0.5
x 315 284 323 287 0 12 B
x 315 302 324 305 0 12 R
x 315 318 324 321 0 12 G
x 316 334 323 337 0 12 Y
162 192 128 256 128 1 1.9 0.0 1.0 0.0
w 256 288 304 288 0
x 195 110 257 113 0 12 Power LED
r 112 256 112 192 0 10000.0
r 160 192 160 256 0 680000.0
x 129 185 173 188 0 12 2N3904
x 201 157 252 160 0 12 Alert LED
r 80 368 144 368 0 470.0
x 140 362 204 365 0 12 Mute Button
w 112 192 160 192 0
w 208 336 208 368 0
x 267 266 328 269 0 12 RJ-11 Plug
w 304 336 208 336 0
s 336 304 400 304 0 0 false
x 341 266 397 269 0 12 RD Power
w 208 336 112 336 0
w 80 304 304 304 0
w 304 288 336 288 0
w 304 304 336 304 0
w 304 320 336 320 0
w 304 336 336 336 0
t 464 160 496 160 0 1 -1.3077158267144877 0.3666244266522099 200.0
w 432 288 432 304 0
w 496 144 496 128 0
w 496 128 336 128 0
x 200 77 432 83 1 24 Smart Cord Simulator
159 432 288 432 224 0
R 448 256 480 256 0 2 60.0 2.5 2.5 0.0 0.5
162 256 176 192 176 1 1.8 1.0 0.0 0.0
w 80 304 80 128 0
w 208 256 208 208 0
w 208 208 192 208 0
w 112 336 112 256 0
t 160 192 192 192 0 1 0.5476910529663741 0.6479168844461276 100.0
w 256 128 256 176 0
w 256 176 256 288 0
g 80 368 80 384 0
g 208 256 208 272 0
g 160 256 160 272 0
g 48 320 48 336 0
x 506 252 576 255 0 12 square wave
w 496 192 496 176 0
g 496 192 496 208 0
w 336 288 336 128 0
x 506 269 585 272 0 12 alert simulator
w 304 320 48 320 0
w 400 304 432 304 0
s 208 368 144 368 0 1 true
x 352 282 387 285 0 12 switch
r 432 224 432 160 0 47000.0
w 432 160 464 160 0
174 144 128 176 128 0 5000.0 0.9950000000000001 Resistance
w 192 128 176 128 0
r 80 112 128 112 0 470.0
w 160 96 160 112 0
w 160 96 128 96 0
w 128 96 128 112 0
w 80 128 80 112 0
x 105 394 121 397 0 12 R1
x 120 252 136 255 0 12 R2
x 168 251 184 254 0 12 R3
x 97 136 113 139 0 12 R4
x 188 197 204 200 0 12 Q1
x 195 390 210 393 0 12 S1
w 336 336 432 336 0
R 496 336 544 336 0 0 40.0 5.0 0.0 0.0 0.5
r 432 336 496 336 0 2700.0
o 6 64 0 34 10.0 0.0125 0 -1
o 52 64 0 34 5.0 0.0015625 1 -1
o 5 64 0 35 2.5 0.025 2 -1
o 33 64 0 35 2.5 0.025 2 -1

**********************

[Samir]

Wow. I haven't seen anything like this since my digital logic lab in college.

[CJR238]

Wow. I haven't seen anything like this since my digital logic lab in college.

X2, even though most of the Digital electronics courses ended up being useless to me its still cool to know.

O, and in short, MEM-TEK is saying use a black magic marker on the inside sticker of the smart cord to dim it.

[MEM-TEK]

Changing out the green power LED's 470 Ohm resistor to a 2K resistor would do the trick, but that ends up dimming both the power and the alert LEDs.

[jsolo]

Mem-tek, very nice!

I do have a question, what is present on the black wire during alert and no alert conditions?

[MEM-TEK]

Mem-tek, very nice!

I do have a question, what is present on the black wire during alert and no alert conditions?

With the SmartCord hook up to my STi, I measured the following voltages on the black wire:

No alert: 0.11V
Alert: 1.68V

The 1.68V in the alert condition makes sense since the black wire is connected between the power and alert LEDs in the SmartCord. Thus 1.68V is the voltage across the alert LED plus the voltage across the collector and emitter in the 2N3904 NPN transistor relative to the green wire.

[jsolo]

Makes sense, sort of.

the .11v is nearly ground, so the black wire is being nearly grounded out during no alert.

Otoh, what if I had an led or led's that needed more forward voltage... Lets say 2V or 3V or more? Although, looking more and more at it, it doesn't really matter what the forward voltage of the alert led(s) is (within reason). It'll just work itself out as a simple voltage divider circuit when transistor Q1 goes into saturation, during which VCE is barely .01V, negligible on the rest of the circuit.

Going this route is safer than trying to guess how much current the ear phone jack can source and/or sink.

With the SmartCord hook up to my STi, I measured the following voltages on the black wire:

No alert: 0.11V
Alert: 1.68V

The 1.68V in the alert condition makes sense since the black wire is connected between the power and alert LEDs in the SmartCord. Thus 1.68V is the voltage across the alert LED plus the voltage across the collector and emitter in the 2N3904 NPN transistor relative to the green wire.

[MEM-TEK]

...Going this route is safer than trying to guess how much current the ear phone jack can source and/or sink.

That kind of was one of my points for posting the SmartCord simulator.

[Samir]

It'll just work itself out as a simple voltage divider circuit when transistor Q1 goes into saturation, during which VCE is barely .01V, negligible on the rest of the circuit.

Umm....yeah....what he said.

[zerbey]

Thank you that is very useful information!