| STATUS: |  |
Contact
Sponsors
| ||||
|---|---|---|---|---|
| Day | Events | |||
| 05/21 Tuesday | 1930 - meetup 2000 Valná hromada | |||
| 05/22 Wednesday | 2200 Elektřina jinak @ Styx smart club = skoro přes řeku od brmlabu | |||
| 05/23 Thursday | 2000 Digital Signal Processing: Reloaded | |||
| 05/25 Saturday | ||||
| Day | Events | |||
This shows you the differences between two versions of the page.
|
project:gsm:shield [2012/09/08 15:12] jenda [brmbora anthem \o/] |
project:gsm:shield [2013/01/12 06:23] (current) jenda [Powering the phone] |
||
|---|---|---|---|
| Line 51: | Line 51: | ||
| The Darlington switch is actually ULN2003A. Single NPN transistor could be used too (peak current is about 200mA), FET probably too. Using Darlington has one disadvantage - the whole phone is at +0.6 (single silicon junction). Fortunately, our FTDI discriminates +0.6V as a correct LOG0. | The Darlington switch is actually ULN2003A. Single NPN transistor could be used too (peak current is about 200mA), FET probably too. Using Darlington has one disadvantage - the whole phone is at +0.6 (single silicon junction). Fortunately, our FTDI discriminates +0.6V as a correct LOG0. | ||
| + | ==== Note on USB hubs and cables ==== | ||
| + | |||
| + | Some USB hubs have a diode between input and output V+. There is a voltage drop of about 0.4-0.5V. Just short the diode, we don't want this drop. | ||
| + | |||
| + | Another voltage drop is on USB cable. Manufacturers tend to save copper, so they use very thin wires. I have seen a cable that had 2 ohms! This is drop of 0.8V at 400mA! The symptoms were simple - two or three phones worked, other didn't. Original FW was complaining about empty battery. Btw. osmocom Hello World FW measures the voltage too. Or just use your voltmeter... | ||
| ==== Driving BTN_DRIVE and PWR_DRIVE ==== | ==== Driving BTN_DRIVE and PWR_DRIVE ==== | ||
