Radio controlled bicycle back light

Project Radio controlled Bicycle back light
A battery powered bicycle back light that can be used to find your bike.
Status	In progress
Contact	Mahjongg
Last Update	2018-04-12

My nephew asked me if I could help him design a school project, a bicycle back light that could be remotely controlled to blink and emit sound.

I engineered a solution around a 315MHz receiver. This is the (fully updated to rev 2.4) schematic.

31 January, 2018, made component placement

this is the component placement drawing as a .PDF : File:Componenten opstelling rf backlight rev 2,2.pdf

this is a 3D rendering of the PCB with the component placement and layout of version 2.2.

J1 connects to the manual on switch J2 connects to the piezo buzzer (now mounted on the PCB) J3 connects to the 3V battery J4 is an optional connection to a commercial 315MHz receiver (for testing).

13 February 2018, made the layout

Added a buzzer (type ABT-407-RC) 12mm round, 6.5mm pin pitch 5.5mm high) moved main LED up to top of PCB Moved mounting holes to 66mm interval added all the copper traces and copper planes created gerber and drill files, and new 3D view. The above 3D picture is now updated, refresh your browser screen if you don't see the buzzer.

Here are pictures of the PCB, left topside, right bottom side. Now with silk screen printing, and with the added static cap and SMT coil of version 2.3

20 February 2018, added final touches

Added silk screen printing, with on silk screen indications for address data for A0 to A7, and copyright text. Changed diode from 1N4007 type to 1N4148 type. updated .PDF and 3D picture (refresh screen if you don´t see it).

Note the eight solder patch locations with which you can configure the "address" of the receiver, underneath the big decoder chip on the bottom left.

6 March, 2018, calculated LC resonance values

Calculated the values for the L and C (C7 or C18 and L3 or L4) of the 315MHz resonance circuit with f= 1/(2 * PI * SQR(L*C)) . Using a trim-cap trimable between 3 and 10pf, (a TZC3R100A110R00 Farnell code 2456140 ) I estimate the average capacity at 6.5pf, meaning the inductance should be about 39nH (see resonance calculator here: http://www.1728.org/resfreq.htm ). I now also found a suitable 39nH coil, (Coilcraft 1812SMS-39NJLC, farnell code 2287131) so I have added a SMT footprint for it. I will also add a footprint for a 0603 cap underneath the trimcap, so I can replace the trim-cap with a fixed one if I want to use a trimable coil instead of a trimable cap.

The new schematic is File:Rfachterlicht rev 2.3.pdf (revision 2.4). The PCB above now shows version 2.4.

April 4, 2018, uploading the production files to Eurocircuits failed

Unfortunately the PCB did not check out when we tried to upload it at Eurocircuits (the PCB manufacturer) Due to some last minute changes. One trace was not connected to the non-trimmable coil Pad, and there were a few via's that did not have enough metal round their holes. I also see a via that doesn't seem to serve a purpose. Initially I thought I could do the repairs on Sunday the 8th, but for some reason that weekend my Asthma became so bad that had no energy at all so I had to stay indoors, perhaps as a result of pollen combined with air pollution. I now hope to do the repairs next Tuesday the 10th.

April 10, 2018, finished PCB

Found the problematic via's were not assigned to GND, so were not connected to the ground plane on the solderside. Not getting a warning about that is IMHO a bug in KiCad's design rule checks. Fixed all layout problems (I think).