Switching RTL-SDR dongles on/off - Page 1
Forum section: electronics / rf-microwave

author: medical-nerd
author_rank: Regular Contributor
timestamp: February 17, 2018, 09:07:49 am
content: HiyaI posted this in the beginners section 10 days ago and have had no replies. Members browsing this section may have advice, since I don't want to fry my dongles. Apologies for the cross-post.I have searched thoroughly and found only one instance of someone trying this.I have 4 rtl-sdr v3 dongles that I am going to connect to an industrial 4 port hub that takes a separate power supply, all of which will be enclosed in a 1u rackmount case - with low noise power supply,cooling, ferrite loaded USB cables, common TXCO etc, etc.Now for the newbie question - I want to be able to turn each dongle on/off as required. As I understand it - the USB A male connector has the power pins longer than data pins so that power is connected first so data pins will not be overloaded by trying to supply power.Is this always true? Does this mean that I can't leave the dongle connected and just switch the vcc line? Do I have to use a 4PST switch for each dongle which may introduce noise ?Cheers

author: Lord of nothing
author_rank: Super Contributor
timestamp: February 17, 2018, 11:03:11 am
content: can you post some Pictures of your setup?I will rebuild my own soon.QuoteWhat do you mean with?

author: medical-nerd
author_rank: Regular Contributor
timestamp: February 17, 2018, 11:25:38 am
content: HiyaThe 4-pole single-throw switches would switch both data and supply lines on/off (one switch per dongle) - I was hoping I could just switch the Vcc line of each dongle (I have plenty of SPST switches...), leaving the data lines connected. Then I would only have to worry about extending one of the lines out of the shielded usb cable.I may go and just overcomplicate the setup using relays, blinken-lights and a microcontroller just for fun.Cheers

author: Teledog
author_rank: Regular Contributor
timestamp: February 17, 2018, 07:41:21 pm
content: KISS method?https://www.ebay.co.uk/itm/4-Port-USB-3-0-Hub-Super-Speed-for-PC-Laptop-on-off-Switch-AC-Power-Adapter/322655451778?hash=item4b1fc37a82:m:m21SAedaoUKv-n4rWwwVOPw

author: medical-nerd
author_rank: Regular Contributor
timestamp: February 18, 2018, 12:13:13 am
content: HiyaThanks for the suggestion, however.....I have used a few of these type of switched hubs now - bought via ebay off UK dealers and from local shops. They have failed within a couple of days. I think that they can't supply more than a few hundred mA even with the power supply connected since using 2 devices powered through the hub fries the hub completely. (2 off portable usb hard drives).None switched hubs seem to be much more reliable.Each v3 dongle will need up to 400mA - This is why I have gone for a 'STARTECH 4200USBM MOUNTABLE 4 PORT RUGGED INDUSTRIAL USB HUB' with a beefy power supply.

author: ovnr
author_rank: Frequent Contributor
timestamp: February 18, 2018, 12:33:05 am
content: Yes, you can just kill the VBUS (+5V) line to each dongle to turn it off. It'd be better to also disable the data pairs, but it should not be necessary. If you want to go down that route, just slap aUSB data muxon each port to disconnect them when not in use.If you run a shared clock, you should turn that off too, or you'll get amusing issues like all the clocks stopping, the clock distribution amp dying, the dongle mysteriously powering up, etc. Just use a distribution amp with individually controlled outputs.

author: dweeb99
author_rank: Contributor
timestamp: March 09, 2018, 02:28:22 am
content: Don't know if this is what you want but I manufacture a USB isolated hub (ISO-HUB) powered by internal LiFePO4 batteries - capable of supplying more than 2Amps in total via the 4 USB VBus herehttps://www.ciunas.biz/product-dets. The ISO-HUB case is a full aluminium so RF shielded by design. the only thing that would be needed is a switch for each USB port but this could be discussed - currently there's an on/off switch for the device.You don't need to switch out the signal lines.The internal batteries are continually charged via connected power supply so there's no concern over battery recharging & these batteries have a lifetime of 10+ yearsAs you can see my devices are all about ultra low noise by eliminating power supply induced noise or noise coming via USB connection. The name of the company Ciunas Audio - Ciunas is Gaelic for "silence or quiet" & I'm based in Ireland & offer a 30 day home trial so your UK location allows low cost return of the small & light device

author: james_s
author_rank: Super Contributor
timestamp: March 09, 2018, 02:30:57 am
content: It should work, but my advice is try it and find out. Simply take an old USB extension cable and hack it, put a switch in the Vcc line and see what it does.