Ideas needed for small footprint program jumpers for Arduino project - Page 1
Forum section: electronics / projects

author: rbm
author_rank: Regular Contributor
timestamp: May 16, 2015, 03:10:00 pm
content: Hi,I'm midway through testing a Digispark Pro-based project, and have come upon a manufacturability challenge that I need help solving.I've designed device using an embedded Digispark Pro. The Digispark Pro requires Data Pins 3 & 4 to be disconnected from any circuitry during programming, otherwise the USB functionality does not work and it cannot talk to the IDE (known design limitation). I've provisioned the board I've designed with a 4-pin JST 1.5 ZH connector that jumpers 2 pairs of pins together. When the jumper plug is removed, the circuitry on pins 3 & 4 is disconnected from the Digispark and programming works. When finished programming, I plug in the jumper plug and the circuitry is reconnected to the computer.It works but manufacturing the jumper plug is difficult and time consuming. Small production runs of this board would not be cost-effective. I hope that someone can suggest an alternative to the JST connector. I need as small a plug as possible to conserve board real estate on an already cramped layout; board size needs to remain tiny.TIA.

author: Kalvin
author_rank: Super Contributor
timestamp: May 16, 2015, 03:26:18 pm
content: I am not sure whether this fits your needs or will ruin your BOM: Two analog multiplexer/demultiplexers in a sot-23, or one CD4053 in SOIC16. A test point on the pcb, when pulled high during programming will disable the switches. When nothing connected to the test point, a pull-down resistor will keep the switches in conducting position.

author: zapta
author_rank: Super Contributor
timestamp: May 16, 2015, 03:33:15 pm
content: Since this for a one time programming of the bootloader, you can use solder jumpers. After the programming you place a drop of hot solder and you are done.IIRC they come in the standard Eagle libraries. If not, look for the sparkfun open source Eagle library.As for attaching the programmer to board, you can use pogo pins.A simpler solution is to use a MCU that comes with USB ISP, such as the NXP LPC11U35. Search for ARM PRO MINI for a sample circuit.

author: rbm
author_rank: Regular Contributor
timestamp: May 16, 2015, 04:06:32 pm
content: Quote from: Kalvin on May 16, 2015, 03:26:18 pmThanks for the idea. I discovered I have to add some input protection circuitry, so the board space after those components are added will not be available.Quote from: zapta on May 16, 2015, 03:33:15 pmNeat. I guess I can use solder wick to pick up the solder blobs in case I need to reprogram the chip at some time in the future. I'll search for the Eagle parts.QuoteI'll research to see if this requires me to restructure my Arduino code, or use a different programming environment. I hope the ARM Pro mini is extremely tiny like the Digispark.

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 16, 2015, 07:17:09 pm
content: +1 to the solder jumper or that 0ohm smd resistor, cant beat the size... otherwise one can use this small dip switch, no need desolder for reprogramming...http://www.ebay.com/itm/10PCS-Red-2-54mm-Pitch-2-Bit-2-Positions-Ways-Slide-Type-DIP-Switch-/281535944316?pt=LH_DefaultDomain_0&hash=item418cd9967c

author: zapta
author_rank: Super Contributor
timestamp: May 17, 2015, 01:50:50 am
content: Quote from: rbm on May 16, 2015, 04:06:32 pmIt's size is constrained by all the pounds that it output. I made once a much smaller one with a subset of the pins but it was not as popular.It's also compatible with mbed.org (tons of libraries) and comes with a fully featured free ide (easy to install on all three platforms), an optional hardware debugger for $20 and is open source so you can use in your own PCBs.The arm architecture has a lot to offer but you need to choose wisely.

author: PeterFW
author_rank: Frequent Contributor
timestamp: May 17, 2015, 02:29:49 am
content: If you want to make it tiny, use a 0402 or 0602 resistor as a solder jumper.You can easily put a solder blop onto that to bridge it and wick it way with some solder wick after you are done.In the eagle library you will find reday made solder jumpers, they are just a bit bigger.