Electronics Forum

by **pebe** » Tue Jun 23, 2015 11:12 am

Yes, you are correct.

by **spawn-ian** » Wed Jun 24, 2015 7:24 pm

Thanks again pebe.

Now starting to get a good idea how this is going to piece together.

I was studying up on the 7805 and there seems to be two standard methods or wiring it in:

[img]http://www.rctech.net/forum/attachments/radio-electronics/1192143d1398867825-traxxas-tqi-blew-up-but-working-7805.jpg[/img]

Or

Some articles place a 0.33uf capacitor before the 7805, and 0.1uf capicitor after the 7805, others have 100nf on both sides.
[img]http://dawn.singlespoon.org.au/7805.gif[/img]

In my mind having the lipo battery as the main power source for the receiver and 3 inverters the draw will be spiking allot, so having the two capictors in circuit will balance out the spikes, but I am unsure if its really needed or overkill and still confused around which capacitor to use.

Also there seems to be alot of conflicting advice around if a heatsink is required or not, as its 7.4 to 5v I can it might get a little warm when in use, but the el wire might be on for 1-2 mins max if waiting at a traffic light or side road so again is it overkill ?

Its so frustrating as I feel am almost grasping the understanding I need, and once it clicks it will be such a simple circuit..

Just wish my dad was still alive, he was a electrition for Marconi/GEC sensors and he would have loved this project, cancer is a cruel thing a miss him almost 3 years... Building a custom motorbike in his memory as well, so all of this is somewhat an emotional journey.

Pebe I see your retired as well, just like my dad was is so nice you take your time to help newbies like me.

by **pebe** » Thu Jun 25, 2015 4:35 am

The caps on either side of a 7805 are there to stabilize its internal circuitry. The values are chosen to give a low impedance at the terminals to prevent the IC from going into oscillation. You can use a higher capacitance if you like – but not lower. I always use a 1uF or 10uF solid bead tantalum on each side. Never use an aluminium electrolytic because they have a relatively high series resistance that increases with age.

I have never used EL wire so had to look up various sources to find its current consumption. This article suggests that 3m of 2.2mm EL wire would draw 80mA from a 4.5V converter.
http://www.thatscoolwire.com/articleDet ... ticleID=67
That being so, the 2.5V voltage drop across the 7805 with 2 wires lit up would generate 2.4V x 160mA = 0.38W, so the IC would not need a heat sink.

Looking further for 5V EL drivers I could only see one 3V – 5V driver and that looked relatively expensive. So if you have not already ordered the bits, I suggest you use this scheme instead:

Use a single 18650 protected lithium cell. That will give about 4V when fully charged, dropping to about 3.2V when discharged.

Use a boost converter like this one to raise the output voltage to 5V to feed the radio receiver.
http://www.ebay.co.uk/itm/DC-DC-Boost-C ... 339f0cf8b6

Use something like this for each of the three indicators you want.
http://www.ebay.co.uk/itm/1M-2M-3M-5M-F ... =undefined
They can be used in constant light mode for the stop lamp, or in flashing mode for the turn indicators. You can discard the battery containers and wire them via the radio switches to the lithium battery via a 1N4001 diode. The diode will drop 0.7V so the battery will provide 3.3V - 2.5V to the driver, which is similar to 2 x AA cells

I hope that helps.

[quote]Pebe I see your retired as well, just like my dad was is so nice you take your time to help newbies like me.[/quote]
Glad to help. It also stops my grey matter from deteriorating too fast!;-)

by **spawn-ian** » Thu Jun 25, 2015 9:26 am

[url]http://www.ebay.co.uk/itm/181725586152?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT[/url]

Found a 5v inverter for £1.61 free postage, its got a USB connector but should be easy to strip the cable back to the +/-.

Will use 1uf solid bead tantalum either side of the 7805 as recommended.

Just need to scetch up a wiring diagram up for Pebe approval before I buy anything.

by **spawn-ian** » Thu Jun 25, 2015 1:42 pm

[url]http://www.aliexpress.com/item/10pcs-16V1uF-1uF-16V-DIP-Radial-Tantalum-capacitor-Free-Shipping/32296850702.html[/url]

would this be a 1uf solid bead tantalum you referenced ?

by **pebe** » Thu Jun 25, 2015 2:53 pm

Yes, that's the one.

by **spawn-ian** » Sun Jul 12, 2015 2:52 pm

The ebay item finally arrived, so will open it up and take some photos..

Also order the below:

3 x 5v EL inverters [url]http://www.ebay.co.uk/itm/181725586152?_trksid=p2057872.m2749.l2648&ssPageName=STRK%3AMEBIDX%3AIT[/url]

2 x 2M Orange EL wire - [url]http://www.aliexpress.com/item/2M-Orange-Car-Flexible-EL-Wire-Neon-Light-Dance-Party-Decor-Light-Flexible-Neon-lamps-EL/32368614391.html[/url]

The EL wire comes with a 3v inverter as well, so I can test this on the Ebay unit I purchased which runs from 2 x 1.5v AAA batteries, just to see if 3v is going to be good enough compared to the 5v USB which is what the voltage I would be using if I built the kit from scratch.

by **spawn-ian** » Sun Jul 12, 2015 3:59 pm

Some pics

Transmitter:

[img]http://i58.tinypic.com/24ya7hw.jpg[/img]

7805 voltage is being used on the transmitter.
[img]http://i58.tinypic.com/1ilx5i.jpg[/img]

Receiver and light unit:

[img]http://i58.tinypic.com/hsm2xh.jpg[/img]

[img]http://i62.tinypic.com/vfdzq8.jpg[/img]

by **pebe** » Mon Jul 13, 2015 8:38 am

Yes, that's right.

by **spawn-ian** » Thu Jul 16, 2015 7:16 am

5v inverters have arrived as well, just waiting on the El wire before I can start testing.

by **spawn-ian** » Sun Jul 26, 2015 9:08 am

Orange El wire arrived, tested at 3,5 and 12 and to be honest I cannot see any difference in brightness, which is a good thing as at least it's no longer an uncertain variable.

El wire as I supspect is not bright enough in daylight, but its fine in dusk/night which is when riders are more at risk.

Just need to decide if I am going to mod the pre built unit or build one from scratch now.