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Previously I was able to modify the Turnigy TGY-i6 transmitter to read the signal strength (RSSI) byte and illuminate an LED near the FPV display if the error rate was high so you could easily tell that it’s probably a good idea to turn around. There was a comment from Paul asking if there was a way to read the RSSI from the receiver itself and then pass this onto the flight controller or OSD.

This sounded like a good idea so I went ahead and did just that with a spare iA6 receiver (I suspect the iA6B should be the same). Firstly lets do a quick teardown of the receiver.


On the top we’ve got our 2 antennas going to the RF can with a microcontroller (TG84023) which would be converting the incoming data to the 6 channels, an 8MHz crystal/oscillator and on the bottom we have another MCU (no label). The PCB marking reads FS-iA6 (Flysky branded), 20130217 and it’s got 3.3V and 5V which I’ve verified so the little 3 or 6 pin packages would be an LDO for 3.3V and DC-DC boost/buck for the 5V and I think the inductor is under the white potting compound.

ia6-rssi-3 ia6-rssi-4

After a bit of probing around, the MCU on the bottom looked to be producing a clock output of 1MHz and some serial data. One initial problem that I thought might be an issue is with syncing the serial data to the clock pulses as at the start and near the middle there is a 4 clock block but it turns out there is an even number of them so it works out just fine.


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The current doorbell we’re using at home is a bit old now and it can play up from time to time (it’s one where you rotate some screws to give a certain combination to link up with the transmitter). A majority of my time for the last few months have been with RC and now I’ve got some spare parts we can put to good use.

My idea is to use a nRF24L01+ with an ATtiny for the transmitter and receiver, an old small video camera bought off Ebay, a 10mW 5.8GHz video transmitter, 5.8GHz receiver, 4.3″ monitor and some batteries. I have some more ideas for the next iteration of this project found at the end.

Doorbell Transmitter


So the first part is the transmitter, I could make an acrylic box with the CNC but it wouldn’t look quite as good as a proper enclosure (though I could stack the layers), a 3D printer would be perfect for this job but since I don’t have one I decided to re-use the enclosure. I took out all the electronics and lined up a button and LED on a veroboard and it fit in nicely.


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Today we’ll be taking a look at a modern device the Synology DS112K Single Bay NAS (Network Attached Storage) which contains a single hard drive with Gigabit Ethernet and 2x USB 2.0 ports. Most of the magic with this device is from the software called the DSM which is a easy to use interface and lets you install additional apps to it, like a download manager, camera surveillance, etc plus third party apps too.

Two screws later and we’re in.

IMG_4205 IMG_4206IMG_4208

Just from the initial view, they spent the time to tape down the fan wire, be it for EMI or tidiness so we can assume there’s a good chance that the quality inside should be pretty good.


We’ve got quite a few DC-DC converters (FR9888, ZT1525) and what look to be some N/P mosfets too (AP4410GM / AP4953GM), one’s near the input jack near a diode possibly for some input protection and 2x P mosfets near a PWM driver chip (uP1504T). They’ve got a cable going to the front panel board tapped down too which just has some LEDs and a button and there’s also a SMD buzzer (AD-7504) which at first glance didn’t look like a buzzer. On the bottom board they have the RTC crystal glued down and have 7 little EMI pads touching the metal case.


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Today we’ll be taking a look at another old device the Netgear ProSafe 802.11g Wireless VPN Firewall (FVG318), it’s a Wireless b/g access point with 1x 10/100 Mbps WAN and 8 ports 10/100 Mbps LAN switch with SPI firewall, the ability to block addresses, services, protocols, keywords, with 8 IPSec VPN tunnels, etc.

IMG_4186IMG_4189 IMG_4187

One screw later and we’re in.

IMG_4190 IMG_4191
IMG_4192 IMG_4193

We’ve got our board with only a few major components so it’s a bit more modern than the last Netgear device we took apart. There’s a ribbon cable with a choke for the front panel lights and an external antenna, there’s the possibility of adding another antenna too. There is a MPS MP1410 SMPS with 3 smaller regulators.


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I’ve mentioned before that I’ve been looking into quadcopters and built my ZMR250 quadcopter a few months ago which is working well, a few modifications have been made here and there; and some are still to come.

IMG_1186_1 IMG_1504_1

One problem with the transmitter is that there isn’t a way that I’ve found to make it beep or light up if you exceed a certain communication error rate, the further you go or the more objects in your line of sight, the higher the error rate becomes. You can glance down at the remote and check it there but when you are focused on your FPV monitor you can easily forgot so I would like a better way. There may be a way to do it in software but I decided to try the hardware route.


To start, I thought I’d go digging around the transmitter to see if I could find an RSSI pin by measuring voltages when I had the receiver on the quadcopter in an open space and then compare to in a microwave (as it blocks most of the 2.4GHz radio). I couldn’t find an RSSI pin so it was time to break out the logic analyser and capture data from the radio module, there had to be some communication between the MCU and radio module in order for it to display on the LCD.


Once thing that was very noticeable was the GOIO pin would pulse low for about 1.2ms every 57ms when it was in range. When the error rate got higher, it would drop to 150ms and sometimes 300ms but after more testing it seemed unreliable.


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Just a quick one today, we’re looking at a generic DisplayPort to VGA Adapter that was reported faulty by an end user, I believe it was lines on the screen/flicking or similar.


We easily pop out the covers on each end.

IMG_1454_1 IMG_1456_1

The DisplayPort connector is directly wired and glued, not too bad.


For the VGA side, we have the PCB with 2 chips but also have 5 wires just dangling around, that can’t be good. PCB Date is 14th January 2014.


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Today we’ll be taking a look at an old device the Netgear ProSafe Wireless Firewall/Print Server (FM114P), it’s a 11Mbps 802.11b parallel print server / access point with 4x 10/100 network ports and 1x 10/100 WAN port.


One screw later and we’re in.


We’ve quite a bit of logic chips under the wireless card and a small heatsink for the processor and an 802.11b Wireless PCMCIA card (XI-325) connected via some right angle pin headers – they may not have had enough room to fit it in or it was easier to buy it off the shelf than design it themselves. For power side of things, we have a LM2576 SMPS and 2x 1084CM linear regulators. PCB date of 35th week, 2002.


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From our last part we looked at the new design for a small temperature logger project with a drafted PCB, the redesigned the voltage switching circuit and USB connect/disconnect feature and updating the data transfer function. In this part, we’ll look the capacitors for our LDO (part of the voltage switching circuit), testing our I2C timing to maximise battery life, switching to a 1Mbit EEPROM and using EEPROM page writes.


Usually when I chose capacitors for a voltage regulator, I’ve never really look at the ESR performance of the capacitor before; I assume most capacitors would be good enough for general loads, most of times they are but I thought it would be a good idea to actually test the ESR this time. The 3.3V LDO I went with was the Richtek RT9166 which is low cost and I’ve use other products of theirs (DC-DC) before so it should be a safe choice.


The input capacitance is 1uF minimum without any ESR requirements and output capacitance is also 1uF minimum (X7R) and we’re given a region of stability depending on the load – 0.3 to say 20 ohms for the small amount of current which I’ll need. I purchased one of the many ESR LCR Meter kits available from Ebay and decided to test a few caps, unfortunately it didn’t measure the ESR of some small caps properly (under 1uF) but it works on larger caps.


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Today we’ll be taking a look at the Lenmar PowerPort Universal Laptop Power Pack, it’s a power pack to provide power to your laptop or device, it outputs 16V/19V and 5V at 1amp and an input plug accepts your laptop’s charger  to charge the Lipo 11.1V / 5500mAh battery. To use the device, you connect your load and press the button which switches the load on.


A lot of little screws later and we’re in.


We have 6x 3.7V 2865mAh batteries with each pair of batteries wired in parallel to give us a 3 cell battery and there’s some adhesive on the case for the inductor to keep that from moving around. PCB date code is Nov 2011.


There’s quite a lot of components, more than I thought would be in it and I didn’t expect to see an ATmega as the MCU. An 0.01 ohm sense resistor at battery1 ground helps to sense current flow so when the button is pressed, the LEDs turn on for a few seconds and if a voltage drop is detected due to having a load connected then it keeps supplying power otherwise after the LEDs turn off, it switches off power. We have 6x R&C branded 220uF capacitors and a 51 ohm resistor with a small 6 pin chip for each battery, I’m guessing it may be some part charge/discharge controller/balancer.


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As part of the Mini Temp Logger design I need to look at a better way of keeping time other than using the watchdog timer as it’s fairly inaccurate. I stumbled across the Microchip MCP7940M Real-time clock controllable by I2C, you can set alarms, a clock output (likely what I might use for my project), ability to trim the oscillator in 1PPM increments (129PPM -/+ range), low power consumption at 1.2uA and the price was $1.

Choosing capacitors

This RTC recommends the use of 6-9 pF 32.768KHz crystals, the most common/cheap ones are 12.5pF and it still does work with them but it won’t be as accurate as the 6-9pF ones (and for me it sometimes stopped working), it took me a while to realise this as I was reading the preliminary datasheet for a while.


The first thing we need to do is calculate the capacitors we’ll require for our crystal, there is a standard formula which we follow for this, Cstray is usually between 2-5pF so lets assume ours will be half way at 3.5pF. I went with a low cost (at the time) EuroQuartz MH32768L crystal that has a CL of 6pF. The best match for our formula is 6pF for CX1 and CX2: (6 pF * 6 pF)/(6 pF + 6 pF) + 3.5 pF = 6.5pF which is close to our CL of 6 but you may have to vary the capacitors depending on your testing.


IMG_1255_1 rtc7

I built a simple PCB for the RTC (doesn’t look the best as I built it about 6 months ago when I didn’t use to sand the PCB) but there isn’t much to it. We just need a crystal with 2 caps, a cap for the chip and then just I2C resistor pull ups. Let’s interface with it, I’ll start off using the Arduino and we’ll move to an ATmega328 later on.


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