Hi, I took it apart (It’s from a radar speed sensor toy) and I have never seen this kind of LCD before. The board has contacts for the lcd where it says lcd1 and the lcd needs to be on those contacts. I took it off and now it’s hard to make it go on again because the lcd contacts need to be exactly on the line outline. The LCD contacts don’t even look like contacts. here are pictures. I alsos see a ATMEGA chip on there maybe by soldering some wires on it we can also get the data.
It’s a radar speed sensor toy from Hot Wheels. I just need to somehow get the data into a photon so I can work with it for this project I am doing to record the speeds and access over wifi. The LCD displays the speed but I need that in the Photon.
If LCD is too difficult Maybe I can somehow connect to the ATmega chip it has as you can see in the 1st picture. Maybe use a voltmeter to find which one is the input to the Atmega and put it in the photon?
No I am trying to measure the speed of large moving objects like cars. I am just using the hot wheels toy mounted on a tripod because it is cheap and actually relatively accurate even though it is a toy.
That LCD connector is what we call a “zebra” connector: there are little fine wires wrapped around a flexible material that just pushes against the board and the LCD. You just need to align everything left-to-right so that the pads on the board and the LCD more or less line up. Normally the zebra connector goes against electro-deposited material on the glass of the LCD on that side, so it can be hard to see where the connections go.
Normally raw direct drive LCDs like that are multiplexed such that there are regions that are driven at the same time due to the slow refresh rates of LCDs. If you have a scope and a lot of free time, you can definitely figure it out. Without a scope, I don’t know how to do it.
Here is a good app note from Microchip on direct drive LCDs:
Hmm, I’d rather go a few steps back and try to figure how the ATmega communicates with the sensor and get into that.
The sensor will provide just a few bytes of actual data (which you are interested in), sends it to the µC, which processes that and then translates it into some form that will be human-readable on the display by adding loads and loads of “decoration” which you are not really interested in.
So you’d catch all that chunk and try to filter out, what you may be able to get access to, before the µC blows it up.
I think @ScruffR’s approach is a good one. This looks like a continuously transmitting RADAR and so at the microprocessor level, you just need to amplify the signal and then basically find it’s frequency. If the frequency is higher than the nominal value when nothing is moving, then a object is coming towards the gun. On the other had, an object receding from the gun will give a value less than nominal. You have to somehow figure out the scale factor from frequency to speed but the precision is pretty low to start with.
That web page you referenced above has good ideas.
Thanks for all the help @bko@ScruffR and everyone else.
After reading that website some more, I read that after filtering and amplifying the radar signal, it is “capacitivly coupled with a 3.3uF capacitor to the first analog to digital converter pin on the microprocessor which is biased at about 12% of the analog supply voltage”. So all I need to do is find that pin somehow and then reroute it to an analog in on the Particle and then have a common ground and do my own doppler effect logic on it right?
On the referenced site, there was a circuit diagram of the amplification and filteriing and it connected to something called AVcc and ADC0.
On the ATmega88 sheet, I read that AVcc is the supply voltage pin for the A/D converter. But then I read ADC is analog input to the A/D converter. Which one is it?
@Nimonster, if the supply on the ATmega88 is 5V, you will need to consider that the max input voltage of the Photon analog input is 3.3v. I’ll need to look at the circuit to see how it could be adapted for 3.3v operation
@peekay123 Oh right, the DAC pin unlike the digital pins is not 5v tolerant. I saw the diagram on the referenced webiste I also have it here. However, I don’t understand why there are 2 inputs to the ATmega. The AVcc and ADC0
None of the A# pins are 5V tolerant when in Analog Read Mode.
I’d say AVcc is the analog reference voltage, while ADC0 is the actual analog sensing pin.
@Nimonster, AVcc is either the reference voltage for the ADC or a filtered Vcc source. Either way, you could power the op-amps with 3.3v from the Photon and the output will have an offset of about 0.38v. I’m not sure what the signal input vs total gain is so I don’t know what the output voltage variation will be.
One thing to note is that the Photon 3.3V output does have ripple which may translate to the output signal Some of the capacitor/resistor pairs act like filters (eg. C7/R4) so they could be tuned to reduce the ripple.
