Quote:
Originally Posted by paulsherwin
Standard USB is 5V 500mA, though higher currents are possible if both the supply and device support it. The cheap Poundland type cigarette lighter plugs are nominally 500mA. Devices need not draw the full 500mA available, and it's perfectly normal for them not to do so.
You can build your own hard wired supply with just a 7805 and a cable with a female USB socket ('receptacle' in USB terminology) on the end of it. Info on USB cable connections is easily available if you google. There are only four wires in a USB 1.1/2.0 cable, a twisted pair for the data and +ve/-ve. You don't need smoothing as such but you will need to decouple the supply with something like 220uF. It's good practice to add a diode to protect the regulator, as shown in the standard datasheets.
https://en.wikipedia.org/wiki/USB_(Physical) |
Thanks, Paul- I knew USB was based on 5v at unit currents ,but not having seen any circuits using a 7805, I was wary .
The idea I had in mind was to use a 7805 from a switched supply ( possibly heater fan supply ,as cigarette lighter is permanently on ) , via a fuse and diode. Dash cam only needs the +& - to run and the cigarette lighter is right next to handbrake and every time handbrake is used, the plug gets moved with possibility of shorting the plug end. I've lost count of number of plug end and car fuses I've replaced. Current won't be a problem as I bought a stack of Maplin 2A 7805 when I had the chance.
As for Scotch locking- a car is not the best place to do IDC type connections. Those of us that have seen the old BT "jelly crimp" and how it corrodes outside the crimp have seen what happens only too well. Far better to either strip back the wire and solder ,only problem is that you need to tape over the joint. I prefer to cut the wire and either solder the three wires together and cover with heat shrink, or crimp two wires into one end and double the other into the other end ,covering the joint with heat shrink.