Performance of A3030E Circuit

We have two prototypes of our A3030E Stage 8 ISL circuit. The photograph below shows circuit E8.1 with all leads loaded, including grounding spring and a temporary white LED for our pre-production tests.



Figure: Un-Encapsulated A3030E Circuit with Programming Extension.

We test all the new features of the A3030E. After a couple of minor modifications, we find these features all work. In particular, the grounding spring and differential amplifier together reduce our simulated lamp artifact to 20 μV, compared to at least 30 mV for the single-ended input of the A3030D. We claim the A3030E with its additional grounding lead will not require a collar seal around the lamp leads where they pass into the head fixture cement.

Antenna Switch: The A3030E shares a single antenna for data and commands. The crystal radio uses the antenna except when the logic chip is powered up and requests the antenna for transmission. This sharing appears to work perfectly, with no loss of either data transmission or reception compared to the two-antenna devices.

Crystal Radio: The new crystal radio layout is more compact. It provides more gain than the earlier 900-MHz crystal radios and extends the reliable command reception range from 50 cm to 80 cm.

Battery Monitor: The A3030E measures its own battery voltage using its spare ADC input channel. We are able to monitor the immediate drop in battery voltage due to turning on the lamp, and the slow decline in battery voltage due to the lamp remaining on. The battery monitor will allow the Neuroarchiver to issue a warning before the battery runs down so far that it suffers permanent damage.

Battery Recharging: We connect the L− to +8 V and the L+ lead to 0 V and charge the battery at a rate of 40 mA through the 75-Ω resistance of the lamp leads. The lead resistance and the charging diode voltage drops complicate the charging process, but with a specially-designed charger, we could re-charge them in the field in less than ten hours. As it stands, we can re-charge them in twenty-four hours with our own power supplies.

Differential Amplifier: The A3030E EEG input is a differential amplifier. In water-filled Petri dishes, a 2-V lamp switching voltage applied to both EEG inputs produced no more than 100 μV lamp artifact. The differential amplifier is, however, vulnerable to 1 MHz switching noise from lamp modulation, which we use to reduce the average power of the lamp. In air, this modulation artifact can be as large as 200 μV, but within a conducting animal body we expect it to be negligible. At 100% brightness, however, this modulation artifact does not exist.

Grounding Spring: The 3030E grounding pads allow us to attach a fifth lead to act as a ground in the tunnel made by the lamp leads as they emerge from the cement of the head fixture. We simulate an animal body with head fixture in Petri dishes. We use a tunnel resistance 100 kΩ, this being the minimum we have observed in our collar seal tests. Without the grounding spring, the separated EEG electrodes pick up 500 μV of lamp artifact. The grounding spring reduces artifact to 20 μV.

We initiated production of more circuits today, and expect to have them next week. We have a few bugs in the logic program to figure out, and the new firmware should provide one battery voltage measurement per second as part of normal operation, using the meta-data channel number fifteen.