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# i wanna make a blood pressure signal generator using purely analog parts. Answered

I found this link : http://www.designnotes.com/downloads/MK105_Assembly.pdf. i was wondering if i could modify this or other suggestions?Or could i just run two together and use a different frequency somehow

needs to look similar to this: http://www.biopac.ca/images/img23.gif
edit:sorry , i was at work and didnt realise that it would be so confusing, so heres a few details

I have access to a 9 Vdc line. using that i need to create a blood pressure signal, where it peaks at 1.2v and lowest is .8V with a slight bounce after thepeak. You can see it in the image that i posted.

i was thinking of using a 555 timer and series of resistors/caps,which i could create a sine wave with it. But how would i go about creating the bounce?

So essentially simulating a perfect blood pressure of 120/80 mmHg , that i could input into my ECG machine or view on an scope.

I am also limited to purely analog. So i can use microcontrollers and the likes. But i am allowed to use 555 timers, op-amps etc.

BTW the ideas that i have seen are great, especially the one using valves and a sewing motor, i cannot use it unfortunately. I might make it during the summer

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## Discussions

I found some information that might be helpful to you. The page discusses a variety of oscillator circuits that produce output sine waves.

It's a bit beyond my knowledge so let me know if this helps at all. :-|

Will do, but i have a few ideas that I'll need to test out. I'll post a circuit and thanks

Incidentally saying " I wanna" when you're older than 4 years old makes you sound like your wailing for an answer like a spoiled child. Grown up language will get you more respect.

These look much more like ramps to me - and certainly that's how I'd synthesise them. Can you use discrete logic ?

Steve

Sorry , the pic isn't the greatest. Imagine it is more rounded and looks a lot more like a sine wave. And discrete logic might be an option, but only in a worst case scenario.

Yes, but it really isn't a sinewave- and if you think for a couple of seconds about HOW the pressure wave is made, you'll see why.

Can you post your exact spec, and I can make some suggestions.

You could do it with two ramps, and some op-amps I think. The spectrum of the signal is too much like hard work to simulate by a Fourier based approach.

Steve

supply voltage : 9vdc
first peak is at 1.2 V
second peak is 1.0V
lowest "negative" peak will be .8V

So my dc offset is roughly 1V
pretty much all i have to run off of

Well, what does a bloody pressure signal look like ?

Steve

Basically I want to simulate blood pressure for use in a class project( making an ECG machine and blood pressure monitor). What I'm looking to be able to use it is to create the proper waveform so i can calibrate

Yes, but the OP is looking for the inverse. They want to build a device (probably some sort of pump with tubing attached) which would make output that looks the same as the pressure variation in your arteries.

Hopefully the OP replies again. There seems to be some confusion among the members about what exactly the OP wants to create.

Oh good grief! Here I thought you were trying to simulate a pulse with a measurable BP that you could practice taking with a BP cuff. Just a signal? You could do that with just a PIC. Simply program tiny steps that increment along the desired wave form. Just like a Maya pyramid used in most inverters. (Modified sine wave)

I'm not sure if I'm reading your notes and updates wrong, and/or I'm just confused, so can you clarify what you have and how you want all this to function?

You mentioned in your update (in the question) that you want to "simulate a perfect blood pressure of 120/80 mmHg , that i could input into my ECG machine or view on an scope". But then you commented that "Basically I want to simulate blood pressure for use in a class project( making an ECG machine and blood pressure monitor). What I'm looking to be able to use it is to create the proper waveform so i can calibrate"

So, do you want to create the ECG machine, or do you already have one? Is it only the signal that you want to create? and if so are you using a blood pressure cuff to create the signal, or is it purely a fabricated type signal that you want to make with other parts (and no software)?

Again, I'm sorry if I'm a little lost on your explanation. (It might just be me). :-|

i already have an ecg/ monitor. i want to create a simulator to allow me to show on the machine a blood pressure signal

Ok. Is the "simulator" a purely fabricated signal, or are you needing to create a pressure cuff type thing to get the reading?

Hmmm. I'll give this some thought. I'm not sure off the top of my head, but thanks for clarifying what your needs are. :)

http://www.biopac.ca/images/img23.gif

similar to that ^

basically two sine waves with a phase difference

Sorry , best way for me to explain. I was thinking of using two sine waves to kinda add into each other when they are offset

Why the limitation on "only analogue" is that a class limit ?

Peristaltic pump.

Or do you just want the sound? and feel

In that case a recording and an inflatable balloon pulsed by Air should work.

To be honest your description of exactly what you want is a bit vague and it's hard to guess so early in the morning.

Sorry, made an edit, hopefully it helps. And a pump cant be used, needs to be electric

If you "just" want an electrical model, what you want is a beast called an "Arb" in the lab - an Arbitrary Function Generator. An Arb lets you design a test signal of just the right shape for whatever, and then apply it with possibly variable frequency and maximum amplitude.

You could synthesise one in an Arduino, using the PWM function - if its fast enough, or you could add a serial DAC and use that (probably easier)

Steve

Hope your up to this one.....you will need..........Either a sewing machine motor with the controller OR a DC motor (the size of your fist) with a pot. Speed control is necessary. A copper/brass/metal/plastic pipe and 2 couplers that have an ID as close as possible to the OD of the drive shaft. JB Weld or similar epoxy. A piece of 3/4" plywood ( 2'X2') and a small length of 2X6 (1'). Wood screws. A large plastic syringe (minimum 1/2" in diameter) Try here (http://www.1topstore.com/en-usd/100ml-plastic-syringe-for-accurate-nutrient-measuring-p14465.html). A spring that will fit over the plunger of the syringe (McMaster-Carr). Some vinyl AND soft rubber tubing. Two small check valves (they must be same I.D. as tubing). First the motor mount: Find a hole saw that is close to the same size as your motor. Measure out about 8", use a compass to draw where a circle towards the upper half. Be certain you have about 2" of material to 3 sides of your circle. AFTER you made the hole, saw the wood across the WIDTH of the hole. You should have two pieces that look sort of like this [][]( )[] The longer piece will mount to your base with screws coming through he bottom =[][]( . The shorter one will clamp onto your motor using screws from the top o)[]= . Place the motor in the cradle but do not permanently mount yet. Make a similar mount for the syringe. Plunger side towards the motor. The drive shaft must be equal height to the syringe. DO NOT install this mount it yet. it may have to move. Next you will have to make a cam from some of the 3/4" ply. Draw the sine wave on a circle of paper and cut it out like a paper doll. Give it a bit of a stretch as you cant have deep valleys on a cam. This will give you an idea of how to shape your cam. Using the pipe to go through the center of the cam and the couplers to hold it at each end. Glue in place. Man this is getting long! Providing you found a spring of proper diameter and strength, place it over the plunger and return the plunger to the tube. The plunger should return ONLY half way. Make a hole in the syringe near the delivery end to accept one of the check valves. The valve must be positioned for return to the syringe. The other check valve goes at he end of the syringe where the needle would be. This will be positioned so that the flow is out of the syringe. Make the hole big enough for the valve to fit. Mount the syringe in its holder and butt up the plunger to the cam at its lowest point. Secure the mount to the base at this point. Use vinyl tube to go to the arm and the rubber tube to simulate the artery. Whew! I think that's it ;)

Love the idea, but needs to be purely electronic. I will look into making this over the summer when i have more time.

Do you need a physical model, like Rick suggests, based on a Peristaltic pump, or an electronic model that make a signal that looks like an ECG trace ?