With four analog inputs on the ssc-32, I would think you could easily run four sensors. If more sensors are needed, then a simple multiplexing setup might be used to monitor a lot of sensors connected to one analog input.
Hi zoomkat
I see the 4 analog inputs but there are only 2 sets of ± pins
How would I do this, having 4 pressure sensors running from my ssc32 would be great.
The ultimate connecton scheme would have been to duplicate the three row setup the Bot Board uses. However there was just not enough room to do this on the SSC-32. So you just have to do a little wiring to get what you want. Have two sensors use one pair of +/- connections. You can use servo wire extenders as a jump start to making the connectors you need.
I’d use one + (or VCC) to supply all four sensors, one - (or common ground) to connect to all four sensors, and then connect the sensor individual outputs to the A, B, C, and D analog input pins. This is based on what I see on the ssc-32 schematic diagram.
This is exactly what I have in mind to do to make my Renesas starter kit board into a robot controller. I’ve ordered several of the single ended servo cables to start this off with and am working on a way to make the board I/O pin connectors into 3 wire setups for sensors and servos. 
8-Dale
Thanks guys !
Ok I am going to try this with 2 fsr using the same + - and separate analog wires back to A and B
Also, can I use the ABB without the chip if i just want it to send sensor data back to the ssc for processing by the computer ?
Thanks
If you are going to use the ABB, you need the MCU on the ABB to handle the sensor data, or create a serial program that will comunicate from your PC to the ABB then to the SSC-32. Either way, you will need an MCU.
How many sensors are you interested in using? Do you have an 8 pin servo control bank on the ssc-32 that is currently unused?
Hello zoomcat
I would like to use 8 sensors if possible.
Yes I have actually 16 thru 31 available, what do you have in mind ?
Wayne
If you can live with a ~.7v loss to the analog input, then you could supply the + to the 8 sensors from the 8 available servo pins. You would use these pins in the byte mode so each could individually be set high at +5v to supply the desired sensor. Between each sensor output to the analog input pin, you would use a diode to prevent back feeding thru the other sensors. A cheap signal diode from Radio Shack has a .7v voltage drop across it, so you would only be able to measure from 0 to ~4.3v, which may or may not be an issue for what you want to do. You can get ~.1v voltage drop diodes, but not at RS. You connect the output of all the diodes to a single analog input pin. When you want to measure the pressure on a sensor, you set the associated servo pin high (with the others set low), and then read the analog input pin to get a pressure value from the sensor.
zoomcat thank-you
Unfortunately I am not a hardware guy so this procedure with the diode while easy for you and others with electronics experience, is very intimidating and probably beyond me at this point. Perhaps 3-4 months down the road, I could attempt this.
As to doubling up the fsr’s, I was able to attach 4 pressure sensors to the ssc and they worked great.
I am now reading up on the ABB for additional sensors.
Thanks to all who helped.
Wayne
I’m not sure about the cost of the ABB, but it is probably more than the $1.39 10-pack of diodes from RS that might solve your problem.
Hi zoomcat
Ok you have convinced me, I will see about getting diodes this week and give it a try. In retrospect this would really make the ssc32 quite flexible.
A couple questions if I may:
What serial command do I send the servo to query it ?
For the pressure fsr is the diode before or after the resistor in the wire going to the analog input pin ?
So if I understand this for eight of the 3-wire fsr’s…
- Supply the + to the 8 sensors from the 8 servo pins.
- The - to the 8 sensors from the 8 servo pins
- Connect the output of all the diodes to a single analog input such as A
Wayne
Powering up and down sensors is not really a good idea as many sensors require several milliseconds to startup and even then the first read value is usually to be thrown away.
ZC is on the right track though. use the port to control a multiplex analogue switch. A 4 to 1 analogue switch would only require the use of 2 bits of a port. The sensors could be powered on continuously and switched and read as required via the analogue switch.
Theoretically, you could run up to 256 different sensors from one eight bit port and one analogue input. Not so good in practice but do-able.
Thanks Paul (PS: also zoomcat)
You have me intrigued now !
Where would I buy such a switch and what description would I look for to know the correct switch to purchase ?
somewhere like farnell or rs components in the uk, radioshack or maplins
just search for “analogue multiplex” on rs components
heres an example
docs-europe.electrocomponents.co … 77fe4d.pdf
its a 4 or 8 way and requires either 2 or 3 bits to control.
They’re used in telephony and modems a lot
Below are the part numbers for the RS diodes. As a first test using your current setup, place a diode between the fs output wire and the analog input pin, with the banded end of the diode going to the analog pin. Run your force test on the sensor and see if the pressure on the fs still produces a useable output. The output should be different (voltage to the pin should be ~.7v lower), but you should be able to detect pressure changes on the fs. Bottom is from the ssc-32 user manual on how to use the byte mode on the servo control pins. For this setup, you would send 1, 2, 4, 8, 16, 32, 64, or 128 to activate the desired pin. As for a multiplexing chip, I like the 74HCT259 chips. RS use to carry these, but no longer. You can get them from the usual electronic suppliers for ~$.50 each.
276-1122 10-pack $1.39
276-1620 50-pack $2.59
Byte Output:
:
=(0 = Pins 0-7, 1 = Pins 8-15, 2 = Pins 16-23, 3 = Pins 24-31.)
=Decimal value to output to the selected bank (0-255). Bit 0 = LSB of bank.
This command allows 8 bits of binary data to be written at once. All pins of the bank are
updated simultaneously. The banks will be updated within 20mS of receiving the CR.
Bank Output Example: "#3:123 "
This example will output the value 123 (decimal) to bank 3. 123 (dec) = 01111011 (bin),
and bank 3 is pins 24-31. So this command will output a “0” to pins 26 and 31, and will
output a “1” to all other pins.
ok thank-you zc
I really like a detailed response and I appreciate that you gave your time to help out.
This is enough info so that I can adjust my code accordingly and I will look for the diodes this week.
Paul
I am also going to try to obtain an analogue multiplex to see how that appproach works.
Thank-you both
Wayne
If you go to some other place other than RS to get the parts, then get a Schottky type of diode like the 1N5818. It only has a .1v voltage drop across it. Below are Jameco prices for various components. The 4066 switch chip combined with the 259 chip might be a cheaper setup than the 7501 multiplex chip by itself. Just as a point of interest, when the force sensor is connected to the analog port and has no force on it, is the reported value closer to 0 or 255?
ad7501 1 for $12.69
Schottky 1N5818 10 for $.70
74hct259 10 for $2.27
74hct4066 10 for $1.67
Hi zoomcat
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