Implantable Lamp circuit project

Posted on Feb 5, 2014

The Implantable Lamp (A3024) is a radio-controlled lamp powered by a battery. Once encapsulated in epoxy and silicone, it is water-proof and compact, so so that it may be implanted in an animal. The A3024 can, in theory, be activated by any sufficiently-powerful source of radio waves. But we plan to activate the A3024 with the Command Transmitter (A3023CT), which produces 146-MHz radio waves. Thus the tuning circuit shown in the S3024 circuit diagram is designed to select power in the neighborhood of 146 MHz. The A3024 is useful in its own right as an implantable source of optical stimulation for gene therapy. It is intended, however, to test the command reception, lamp power generation, and light delivery of the Implantable Sensor with Lamp (ISL). The A3024 provides 5-V power to an LED through its L+ and L− pads. These must be connected to two leads with resistance suitable for driving the lamp with 5 V. If the forward voltage drop of the LED is 3.1 V and we want 20 mA current, the lead resistance should be around 100 Ω.

Implantable Lamp circuit project
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Implantable Lamp circuit project - image 1
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In the ISL Conceptual Design, we proposed to use the L+ lead as an antenna for command reception. But this turns out to be impractical. The input impedance of our tuning circuit is around 10 kΩ. In order to force 146-MHz power to pass through the tuning circuit rather than into the lamp power supply, we would need a 10-μH inductor with self-resonant frequency 150 MHz or higher on both the L+ and the L− inputs. We can't find such an inductor in a surface mount package. The A3024 provides two pads for a small loop antenna. One is connected to the tuning circuit, the other to the circuit ground. Now we see a peak response at almost exactly 146 MHz, and using component values that agree with our calculations. But we note that the peak voltage is only 65 mV, and this is after we fiddle with the antennas to get the biggest signal. We obtained 120 mV at 146 MHz with not fiddling when we had no tuner. We try again to activate the lamp with the antenna of an A3019E. We see no sign of the A3019E transmission in VR. Whatever signal the A3019E induces is less than 2 mV. The lamp will not turn on. We measure reception range for the same antenna orientations and power. We see the lamp flashing at range 12 cm with our tuning circuit in place, 13 cm with the tuning circuit removed, and 17 cm when we cut off the extension circuit, load a BR1225 battery, and leave off the tuning circuit. [17-JAN-13] After clipping off...

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