If the E3 has a TTL serial port as reported here then a USB to TTL serial adapter should work fine. No need for line drivers or level adjustment, nor any need for inverters. Just connect it straight through. These USB to TTL serial are very common and cheap because they don't have the MAX232 (or similar) conversion chips. Wire:
GND --- GND
TX --- RX
RX --- TX
Do not use a real RS233 port as it will use higher (and lower) voltage and be inverted.
These cheap USB serial devices are a couple of quid on eBay.
Walt