SMD Soldering practice kit instructions - Page 1
Forum section: electronics / beginners

author: hamster_nz
author_rank: Super Contributor
timestamp: November 30, 2017, 12:47:57 am
content: In the 11/11 sales I purchased a few of the $0.99 (with free shipping) SMD soldering practice kits that arrived yesterday.https://www.aliexpress.com/item/2016-New-Both-Sides-SMT-SMD-Electronic-Component-Welding-Practice-Board-PCB-Soldering-DIY-Kit-Skill/32595680463.htmlThey are nothing too exciting - a NE555 connected to a CD4017, a few transistors and diodes, and plenty of LEDs and resistors and a couple of caps - around 50 parts in all on the active side. On the back side they have "bonus challenges" - 0603, 0402, and some resistor packs.However... the instructions are in Chinese. That's not a problem for me, as I've worked from the schematic without any issues.If anybody is keen to give it a try, but being held back by the lack of English instructions then let me know and I'll spend some time making some English ones.

author: kalel
author_rank: Frequent Contributor
timestamp: November 30, 2017, 01:01:39 am
content: If you tried one, what did you use to do the soldering?

author: hamster_nz
author_rank: Super Contributor
timestamp: November 30, 2017, 01:21:11 am
content: Just a bog standard 45W temperature controlled iron, with a 2mm conical tip, & 0.71 mm solder wire. Would not do the 0402 with this though, I would put in a 0.5mm tip and consider using paste.I did have to get my second iron out to to swap around an LED I put on backwards...

author: kalel
author_rank: Frequent Contributor
timestamp: November 30, 2017, 01:27:17 am
content: Quote from: hamster_nz on November 30, 2017, 01:21:11 amGood work, I would probably need more practice, then, there's only one way to learn... Those kits are relatively cheap (and so are custom PCBs these days).

author: rthorntn
author_rank: Frequent Contributor
timestamp: April 03, 2018, 05:13:15 am
content: I just got some of these, hamster_nz could you do some instructions please?

author: hamster_nz
author_rank: Super Contributor
timestamp: April 03, 2018, 08:28:48 am
content: Here is the very rough English instructions:Theory of operationThe NE555 timer is set up to run as an astable oscilator, with a frequency determined by R48, R49 and C27.f = 1.44/((R48+2*R49)*C27)f = 1.44/((1000+2*2000000)*0.0000001)f = approx 4 HzThe output of the NE555 drives LED D1, with R50 controlling the current through the LED.It also drives the clock input of the CD4017 decade counter. Only ne of the outputs of the counter (Y0-Y9) is on at any time, and then each time the clock signal rises it moves on to the next output - taking 10 cycles to return to the original state. Each of the 10 outputs drive an LED, through a current limiting resistor.The CD4017 also has a "carry output" Is the input divided by 10, and goes from low to high when the selected output wraps from Y9 back to Y0. This output is used to drive four transistors, which in turn drive the four LEDs in the corners of the board. The four diodes are not functionally significant, but R61-R64 limit the current into the transistor, and R65-R68 limits the current through the diodes.Parts listCode:QtyValuePkgPart1Circuit board48x60mmPCB1NE555SO-8U11CD4017SO-16U220.1uF Capacitor0805C27, C2811Red LED0805D1-D114Blue LED0805D11-D1541N4148L34D13-D154S8050SOT-23Q1-Q412M Resistor0805R4915470Ohm Resistor 0805R50-R68Additional parts (for the back of board, not actively used):Code:QtyPartPkg81206 Resistor1206200603 Resistor0603200402 Resistor04026Resistor array0603*4AssemblyStep 1- Identify R49 (2M Ohm Resistor - marked 205) and solder in place- Identify R48 (10k Ohm Resistor - marked 103) and solder in place- Identify C27 & C28 (0.1uF Capacitors - unmarked) and solder in place.- Solder the NE555, taking care to orient it correctly.- Identify R50 (470 Ohm, marked 471) and solder in place- Identify the LED D1, and solder in place. Take care to orient the green stripe to the striped end- Attach some power wires to the + and - pads, to allow it to be attach to your power sourceTest - the LED should blink a frequency of about four times per second. The most common problem the LED is the wrong way round,Step 2- Solder on U2, taking care to orient it correctly- Solder on LED D2, taking careful note of orientation- Solder on the R51 (marked 471) resistor for the LED- Test - it should come on briefly once every 2.5 secondsStep 3- Solder on the rest of the LEDs and resistors in the circle.- Test - all the the LEDs should light in sequenceStep 4- Solder on the four diodes D12 - D15- Solder on the four transistors, Q1-Q4- Solder on the four remaining 470 ohm resistors, R65-R68- Solder on the four remaining LEDs, D16-D19- TestProject Complete!

author: rthorntn
author_rank: Frequent Contributor
timestamp: April 04, 2018, 04:00:23 am
content: Fantastic, thanks hamster_nz!Does anyone want to have a crack at helping a beginner out?So I get that you need resistors to stop the LEDs taking too much current (r50-r60?)I also get that you setup the timing of the 555 with resistors (r48 r49?)The 555 output is 4Hz which feeds the CD4017, so 4 a second, so that lights each LED in sequence, the sequence should complete in 2.5 seconds?What is D12-D19, R61-R68, D16-D19 & Q1-Q4 (why NPN transistors, what are they doing, amplifying, switching?) for, its connected to "carry out" (it completes one full cycle for every 10 clock cycles, hamster_nz has it's the input divided by 10, I'm confused about this?), what exactly is happening here, why 8 resistors, what does the "four diodes are not functionally significant" mean, what do the four LEDs do here - flash every 2.5 seconds?Thanks all!Richard

author: hamster_nz
author_rank: Super Contributor
timestamp: April 04, 2018, 04:09:16 am
content: Quote from: rthorntn on April 04, 2018, 04:00:23 amCorrectQuoteThe pin on the decade counter is not designed to drive enough current to light all four LEDs, so Q1-Q4 act as switches. Four resistors limit the current flowing into the base of the transistors, and the other four limit the current through the LEDs when they are lit.The four standard (non-light-emitting) diodes don't have any real purpose. the circuit will run just fine if they are replaced with wire links or solder bridges. I guess they are there so you can experience the fun of soldering the diodes in small round glass packages.

author: rthorntn
author_rank: Frequent Contributor
timestamp: April 04, 2018, 04:34:53 am
content: Perfect, thanks, last question D16-D19 what frequency do they flash at?

author: rthorntn
author_rank: Frequent Contributor
timestamp: April 04, 2018, 06:30:14 am
content: Also is D12-D15 purpose to block the flow of current in the reverse direction? Thanks!

author: hamster_nz
author_rank: Super Contributor
timestamp: April 04, 2018, 11:52:01 am
content: Quote from: rthorntn on April 04, 2018, 04:34:53 amThey flash at the same frequency as the circle of LEDS - 1/2.5 Hz. The interesting thing is the duty cycle. Take another look at that CD4017 waveforms from the data sheet you included a few posts back. It should make it all clear.Quote from: rthorntn on April 04, 2018, 06:30:14 amIf assembled correctly, there is no chance of the emitter on the transistor getting much higher than 0.7V, and even then that will only occur when the diode is forward biased. I really can't imagine any reason for them being there, apart from soldering practice.

author: rthorntn
author_rank: Frequent Contributor
timestamp: May 07, 2018, 07:40:02 am
content: Edit: I can get continuity on on side of R48 but not on the other side.Hi All,Please be gentle, my first attempt at SMD soldering, haha, it doesn't work at the end of step 1.Using a Hakko at 320C with 60/40, I'm not adding extra flux.If someone can spare the time please take a look, looking for theories, tips or what I could do to troubleshoot with a DMM?I potentially destroyed something with heat, the components just move around when I get near them with the iron.I accidentally attached U2 (not sure if it matters)I got 20 of these kits so I will keep practicingThanks for looking.Richard

author: hamster_nz
author_rank: Super Contributor
timestamp: May 07, 2018, 08:37:33 am
content: Hi RichardR50 doesn't look to be attached at both ends.Do you have any 'realy good' tweezers? I find mine invaluable. The are so hard and sharp that they are dangerousHere is my process....0. Iron about 280.1. Tin one pad. The quantity of solder on the diode pads loots fine. (If I tin both I can never get the part to sit flush).2. Place and hold part with tweezers.3. Solder the tinned pad by just heating it4. Check, reheat and adjust if needed.5. Then solder the second pad, using more solder wire.6. Reheat the first pad till it melts. If the part moves then the solder at the other end hasn't wetted correctly.7. Solder any other pads (eg transistors, ICs)I still need wick and/or a flux pen on the ICs more often than not..As they now say in school... Practice makes perfect!

author: hamster_nz
author_rank: Super Contributor
timestamp: May 07, 2018, 09:13:22 am
content: Quote from: rthorntn on May 07, 2018, 07:40:02 amIt is only fair that you can chuckle at my soldering too (it is the blind leading the blind). The local shop only has 0.7mm solder, and I always end up with too much on the joint!

author: rthorntn
author_rank: Frequent Contributor
timestamp: May 07, 2018, 09:21:25 am
content: Thanks hamster_nz! Could you please post a picture of an entire soldered board so I can use it for reference?I can get continuity on one side of R48 but not on the other side, should I be able to get continuity through a 10K ohm resistor?

author: hamster_nz
author_rank: Super Contributor
timestamp: May 07, 2018, 09:33:36 am
content: Top row (with black on the '-' pad.R48 5VR50 jumps aroundR49 Jumps between 1.3V and 3.8VC28 Jumps around.C27 0VOther endsR48 Jumps betweem 1.3V and 3.8VR50 Jumps aroundR49 mostly around 2VC38 around 3v3C27 Around 2.5V (jumping)555 pins1 0V02 Jumps around (same as pin 6)3 Jumps4 5V05 3V36 Jumps around (same as pin 2)7 Jumps aroundu 5V0

author: hamster_nz
author_rank: Super Contributor
timestamp: May 07, 2018, 10:07:58 am
content: Quote from: rthorntn on May 07, 2018, 09:21:25 amSee attached.QuoteA 10k is too high to pass a continuity test.

author: rthorntn
author_rank: Frequent Contributor
timestamp: May 08, 2018, 06:23:06 am
content: Thanks, Pin 8 on the 555 wasn't connected well enough, I added a dab of solder and it works!