Desk cable tidies
Anyone building a bespoke office desk will be faced with the issue of how to organise the plethora of cable and flexes associated with a modern office, notably for computing equipment. Any commercially obtained office desk is likely to have a hole in one corner of the worktop to allow the passage of cables from a keyboard / mouse / telephone / desklamp etc etc, and this will be lined with a plastic 'grommet' or desk cable tidy. These typically have an inset adjustable cap, to accomodate different sizes and bundles of cables, and are deliberately large enough to accept at least a standard UK 13A plug:
A 1/2" - 3/4" gap between the rear of the desk and the wall also works as a full width cable port. It is more flexible but not as elegant as a recessed port.
Using the PC's Power Supply
Many computer accessories powered from wallwarts can more tidily be powered from the computer's built in power supply. PC supplies deliver 12v, 5v and 3.3v. To connect an accessory to the computer sometimes requires a molex connector, and it means opening the cover to plug it in.
- 5v runs 5v and 6v appliances, such as small speakers
- 5v appliances can get power from a usb plug, as long as they're not too power hungry
- 12v runs 12v appliances and larger speakers (12-16v) which are not voltage critical
- 3.3v runs portable devices that use 2x 1.5v batteries, eg music players.
- The 12v PC line can also supply any voltage between 5v and 12v if series dropping diodes or a voltage regulator are used. It is simple to produce 9v by using 3 series diodes.
How Much Power
There are limits to how much power you can draw from the PC's supply, but there is little likelihood of reaching those limits with a modern PC. The days of the 486 with a 120w PSU are long gone, but there are some modern low power machines around that can happily run small speakers on 5v, but beyond that its a case of try it & see.
Sometimes running speakers on the pc's power supply causes audible noise superimposed on the audio. If you encounter this noise, you can either stay with a separate power supply, or use some of the following ways to reduce it:
- Make sure you have good firm connections, wires just twisted or wrapped together is no good.
- Move the molex connector supplying the speaker from a computer power supply lead shared with another device (eg hard drive) to a lead coming direct from the PSU with no other item powered off that lead
- Connect an extra capacitor on the power rail next to the speakers. A 1000uF or 2200uF electrolytic cap plus a 0.1uF ceramic cap is good.
- Turn volume knob on speakers down and PC volume control up.
- Replace thin wire with thicker for the power lead to speakers
- Bolt the PC end of the power wire -ve to the chassis instead of the power supply connector.
Note that powering audio devices (e.g speakers or mp3 players) from the PC's supply may give poor results with lots of noise superimposed on the wanted sound because the ground wire for the audio signal is now in parallel with the power supply ground wire which is connected to a different point inside the PC, and there is likely to be electrical 'noise' between the two ground points which will be superimposed on the wanted audio signal. Whether this is a problem is a matter for experiment but it is advisable to try a quick hook-up to find out before committing to such an arrangement.
Note: If you intend to use a stand-alone power supply (i.e. one not powering the PC), if its an ex-pc supply you may need a dummy load on the 5V to draw enough current to allow the power supply to operate. You would also need to connect the right wires together to make it power up.
Trimming flexes to the length needed can reduce the amount of flex on show significantly. but can be inconvenient later. This approach works best with plug in leads, which are easily swapped.
2 Way Leads
Some leads are available in 2 way versions. These have 2 leads and one mains plug. Often the lead is Y shaped. These reduce plug, socket, flex, and sometimes extension lead use. These leads are available ready made in 3 and 4 way formats too.
These leads are only recommended for appliances that stay in the same place, as use on mobile items could result in unplugged plugged-in connectors lying on the floor.
2 way leads may be safely made from existing leads by putting 2 leads into one mains plug, provided that both flexes are of the same size, both fit the plug (some plugs have enough space, some don't), and both are gripped securely by the cord grip.
Compact Multiway Sockets
As well as standard 13A multiway sockets, compact multiway sockets are available which use a smaller type of connector, such as IEC connectors, Bulgins, and others. These reduce space use, but require you to fit a plug to your leads that you wont be able to plug in elsewhere, and this is somewhat inconvenient if you move an item later. These units also cost significantly more than standard multiway extension leads.
Some people like to use these, but I've found them inconvenient and too expensive to use all round the house.
The one variant of these that works relatively well is ones with IEC plugs & sockets. Ready made leads with IEC plug to IEC socket exist which can be used with these, and if an appliance is moved one simply plugs a standard IEC lead into it instead.
Any appliance that does not use an IEC lead will still need an IEC plug fitted, and be unpluginnable elsewhere. One way to resolve this is to run only IEC leaded appliances off the multiway block, and run other appliances on standard 13A mains plugs.